Many of these terms have a long history and their meanings have changed over space and time. I have given those definitions I think most suitable in a mediaeval West Highland context.
adze – axe-like tool for shaping wood, especially in shipbuilding
backstay – rope from stern to masthead to help secure mast
bail/bale – to empty water out of a boat by hand, usually by means of some sort of scoop or bucket
bark/barque – general term for a sailing-ship
birlinn – (Gaelic) a general term for a West Highland galley. It derives from byrdingr (Norse) which was a small cargo-ship built with the lines of a longship rather than a knorr
boat-ell – a measuring-stick used in boat-building (an ell is a measure of length)
bonnets – additional pieces attached to the foot of the sail
braces – ropes attached to yard in order to change its angle
brails – ropes to edges of a sail for taking it in
carvel – a method of building ships by constructing a frame or skeleton first and then adding a skin of planking. Each strake lies flush with the next, not overlapping as with clinker. It is more usually associated with Mediterranean than with Northern ships
caulk – to insert a fibrous material into the seams between planks to make them watertight
clench/clinch-nail – the nail holding two overlapping planks together, hence the word ‘clinker’. The nail is driven through the wood and a metal rove hammered over it from the inside. The point of the nail is then bent over to clench nail, wood and rove together.
clinker – a system of building the skin of a boat by a series of overlapping planks – each of which is ‘clinched’ to its neighbour. The keel and skin are constructed first, the internal framework fitted subsequently.
cog – a boat-type distinguished from the Viking type by its flat bottom and sharp angles between the keel and endposts.
coracle – small skin and wicker boat, now mainly associated with Wales – for inland use
creach – (Gaelic) plunder or pillage, often in the context of a cattle-raid
crear/crayer – small trading vessel (term used from about fourteenth century)
crompstre/crompster – a small ship, a kind of galley
currach/curragh – skin (now canvas) and wicker boat, usually larger than a coracle and certainly sea-going
double-ended – a boat with symmetrical ends, i.e. the stem is the same shape as the stern
forecastle – fortified structure at the stem of the boat. In the sagas the forecastle-men were amongst a boat’s foremost warriors.
forestay – rope from stem to masthead to help secure mast
freeboard – the height from the lowest point of the gunwale amidships to the waterline
furl, furled – the process by which a sail is rolled up and hung in bunches from the yard
galley – a general term for a boat that can be rowed as well as sailed
garboard – the line of planking next to the keel
grommet – a loop of skin or fibre to attach the oar to thole-pin or gunwale
gudgeon – ring into which the rudder pin or pintle slotted. The gudgeon was fixed to the stern-post whereas the pintle was part of the rudder
gunwale – timber fixed along the sides of a boat above the top line of planking
halyard/halliard – rope to haul up the yard and sail
hulc/hulk – a boat-type with a distinctive curved or banana-shaped hull
hun-bora – pierced wooden bole at the top of the mast on a Viking ship. The halyard ran through this and the bulbous expansion also served as a fixing-point for other ropes.
keel – main structural timber running lengthways along the bottom of the boat or a general term to describe clinker boats built within the Viking tradition
keel-scarf – the scarf or join in a keel which was made from more than one piece of wood.
knorr/knarr – substantial Norse cargo-ship
land/plank-land – where two clinker strakes overlap
larboard/ladeboard – left-hand side of boat when looking from stern to stem. Since the early nineteenth century this term has been replaced by ‘port’ to avoid confusion with the word ‘starboard’.
lee – the side away from the wind
leech – the side or vertical edge of a square sail
limmar/lymmer – rogue
liripipe – the long hanging tail of a hood or cowl – (as worn by helmsmen in mediaeval illustrations)
lymphad – anglicised version of Gaelic ‘longfada’ or longship where ‘long’ = ship and ‘fada’ = long
mast – vertical timber to carry yard and sail
mike – wooden crutch or support which helped to stow mast, spars or oars out of the way on board ship
naibheag/nyvaig – Gaelic, literally little-ship
naust/noust – a boat-house, ship-building yard, or bank-cutting for the winter-shelter of a boat.
oakum – fibre used in caulking, usually obtained by unpicking old rope
oarports – holes below the gunwale through which the oars could be passed for rowing
parrel (or traveller) – ring of wood and rope which kept yard attached to the mast
paying – treat planks with pitch or tar etc. to protect against effects of water
pennon – flag, often with trailing triangular tails
pintle – downward-pointing pin on rudder which slotted into the gudgeon on the sternpost
plank – wooden board, one or several of which made up a strake along the side of a boat
port – left-hand side of boat when looking from stern to stem
portage – the carriage of boats or freight across a piece of land separating two stretches of water
quarter-rudder – another term for side-rudder
reef – the business of shortening or reducing a sail by tying up reef-points or reef-laces with reef-knots. Reef-bands are reinforcements in the sail material to help it take the extra stresses.
robands – small pieces of rope through eyelets in the top of the sail which were used to tie it to the yard
rocker – the amount of spring or upwards curvature in the shape of a boat
roves – little washers or plates of metal impaled on the point of a clinch-nail which was then bent over. In this way they helped ‘clench’ the nail, and the planks, in position
rowlocks – either a U-shaped space cut into the gunwale or (now) a metal crutch fitted to top of gunwale to act as fulcrum for an oar
rudder – board or oar for steering, placed either at the side or at the stern of the boat
scarf – a joint between two pieces of timber
sheer – the upward curve at each end of the boat
sheet – line to lower (lee) corner of sail
shrouds – ropes to support the mast (across the boat) – in Highland galleys usually secured inside the boat amidships
side-rudder – rudder fixed forward of the stern, usually on the right or starboard side of the boat
sorning – exacting free quarters and maintenance at expense of others.
square sail – sail set at right-angles to the centreline of the vessel
starboard – literally ‘steering-board’ side, or right-hand side of boat when looking from stern to stem
stem – bow or front of boat
stempost – the endpost at the bow of the boat
step – to put the mast up and into its base fittings
stern – aft or rear of boat
sterncastle – fortified structure at the stern of a boat
sternpost – the endpost at the stern of the boat
stern-rudder – rudder fixed at stern of boat
strake – line of planking forming part of side of boat
sweep – long oar used in some boats for steering
tack – line to lower (weather) corner of sail
tallow – animal fat
thole-pin – pin acting as pivot for oar, to which it can be secured by an oar-loop (grommet) or via a pierced block of wood on the oar (bull)
thwarts – cross-timbers which can also be used for seating
tiller – a wooden arm for holding and steering the rudder
topcastle – fortified structure at the top of the mast
trenails/treenails – wooden pegs or dowels used to fix timbers together in boatbuilding
unstep – to take a mast down
wadmal – a coarse, homespun wool used by the Vikings for sails
windlass – machine for hauling or hoisting rope etc.
yard – wooden spar from which was suspended the sail. It was spread horizontally in Highland galleys.