noun

caulk

kawk

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Caulk (noun) means a flexible waterproof filler squeezed into joints and gaps — around baths, sinks, window frames and skirting boards — to seal them against water and draughts. Example: “Run a bead of caulk along the edge where the bath meets the tiles.”

noun

A flexible waterproof filler squeezed into joints and gaps — around baths, sinks, window frames and skirting boards — to seal them against water and draughts.

"Run a bead of caulk along the edge where the bath meets the tiles."

"The old caulk had gone mouldy and needed scraping out."

verb

To seal a joint or gap by filling it with such a compound.

"Caulk around the window frame before you paint it."

"He spent the afternoon caulking the shower tray."

nautical In traditional boatbuilding, to drive fibrous material such as oakum into the seams between a wooden hull's planks to make it watertight.

"The shipwrights caulked the seams with oakum and hot pitch."

How to use caulk

Learner’s notes

In plain EnglishSquishy waterproof filler you squeeze into gaps so water cannot get through.

When to use it

Neutral. Everyday in DIY and trade contexts; the noun is more common in American English than British, where sealant dominates.

Memory tip

Caulk fills the flexible joint where two different surfaces meet; grout fills the rigid gaps between tiles. Using grout where caulk belongs causes cracking.

Trace the full origin ↓

Easily confused with

grout → sealant → putty → cork →

Common pairings

a bead of caulk caulk gun silicone caulk caulk the seams apply caulk

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C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

Test yourself on “caulk” A quick quiz — meaning, synonyms & usage →

Fill the gap

Can you complete this real example?

Run a bead of _____ along the edge where the bath meets the tiles.

Etymology

From Old North French cauquer, from Latin calcare 'to tread or press down', reflecting the original sense of pressing material into a ship's seams.

Origin: Latin

Synonyms

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sealant filler mastic seal fill weatherproof caulking calk

Related words

people close meet fit shut fill empty load

Frequently asked questions

What is the difference between caulk and silicone?

Silicone is one type of caulk, not a rival product. Caulk is the general word for a gap-filling sealant; silicone caulk stays flexible and waterproof so it suits baths and showers, while acrylic or latex caulk can be painted over and suits skirting boards and trim.

Is caulk spelled differently in Britain?

Both caulk and calk appear historically, but caulk is now standard everywhere. In British usage the product is just as often called sealant or mastic, and the tube is bought as bathroom sealant rather than caulk.

How is caulk pronounced?

It rhymes with talk and walk — the L is silent. Saying it as kalk is a common misreading.

What is the meaning of caulk?

"caulk" (noun) means a flexible waterproof filler squeezed into joints and gaps — around baths, sinks, window frames and skirting boards — to seal them against water and draughts.

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