What does calk mean?
Calk is a verb meaning to make a boat, window, tank, or other structure watertight by driving or applying a waterproof material — traditionally tarred oakum or pitch, today silicone or polymer sealant — into its seams and joints. It is chiefly associated with wooden shipbuilding, where calkers (or caulkers) drove fibers between planks to keep hulls dry, but it extends naturally to plumbing, masonry, and everyday home repair, where one might calk a bathtub edge or window frame. In American English, calk is now essentially a variant spelling of the more common 'caulk'; the older form persists in maritime and historical writing. A second, older sense refers to a pointed metal projection on a horseshoe that gives traction on ice or rock, and to wounding a horse's foot with such a projection. The word derives ultimately from Latin calx, the same root that gave us chalk, calcium, and calculus.
To make a structure watertight by filling its seams or joints with a waterproof material such as oakum, tar, or sealant.
"The crew calked the deck planking before the long Atlantic crossing."
Now commonly written 'caulk'; the calk spelling appears mostly in nautical and historical texts.
A pointed projection on a horseshoe, providing grip on slippery ground.
"Winter shoes were fitted with sharp calks to prevent the horses from slipping on frozen streets."
Also spelled 'calkin'; the corresponding verb sense means to lame a horse by striking its foot with this projection.
Used only for the noun sense (horseshoe projections); the verb has no plural form.
"The farrier replaced the worn calks on all four shoes."
The humble word 'calk' shares an ancient root with 'chalk', 'calcium', and even 'calculus' — all tracing back to Latin 'calx', meaning limestone or heel.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of calk
Calk entered English in the late Middle Ages from Middle Low German or Dutch forms of a verb ultimately derived from Latin calx, 'limestone' or 'heel', via the Latin verb calcare, 'to tread'. The sealing sense likely arose through the notion of treading or pressing material firmly into seams, while the horseshoe sense relates to the 'heel' aspect of the root. The same Latin root produced 'chalk', 'calcium', 'calculus', and 'recalcitrant', making calk part of a remarkably broad word family. Its modern spelling 'calk' competes with 'caulk', which has become the standard form in most current dictionaries.
Related word forms
How calk is actually used
In contemporary American usage 'calk' is largely a variant spelling of 'caulk', which dominates both British and modern US writing. The older spelling survives mainly in nautical, shipbuilding, and historical contexts. As a noun referring to horseshoe projections, 'calkin' is often used instead. The word carries a practical, craftsmanlike connotation rather than any formal register.
Easily confused with calk
'Caulk' is simply the more common spelling of the same word in modern English, especially British usage; they are interchangeable variants with identical meaning.
A 'calque' is a word or phrase borrowed into one language through literal translation of another (a linguistic loan translation), whereas 'calk' means sealing seams to make something watertight.