What does crud mean?
"Crud" is an informal English noun for any unpleasant, dirty, or unidentifiable substance — the greasy film on a stovetop, the sludge at the bottom of a neglected container, or the grime scraped from machinery. Its strength lies in its vagueness: when something is too messy, sticky, or revolting to name precisely, "crud" covers it. The word carries a mildly comic, dismissive tone and appears almost exclusively in casual speech; formal contexts call for terms such as "residue" or "sediment" instead. It also has an older, chiefly American sense as slang for a minor unspecified illness — catching "some kind of crud" — which survives today mainly in phrases like "feeling like crud". The word traces back to early twentieth-century American military slang, where it referred to disease before broadening to mean filth generally. For writers seeking a vivid, down-to-earth alternative to clinical vocabulary, "crud" is a useful and expressive choice.
An unpleasant, sticky, or filthy substance; dirt, residue, or unidentifiable gunk that accumulates on surfaces or inside containers.
"The mechanic wiped years of grease and crud off the engine block."
Informal register; avoid in technical or formal writing, where "residue", "sediment", or "deposits" are preferred.
(Informal, originally US military slang) An unspecified minor illness or a general feeling of being unwell.
"Half the office was out with some kind of crud last week."
Chiefly American and somewhat dated in the strict medical sense, though phrases like "feeling like crud" remain common colloquially.
Rarely pluralized; "crud" usually refers to an amorphous mass or a general condition, so speakers typically say "the crud" or "some crud" rather than counting discrete units. When multiple distinct kinds are meant, "kinds of crud" reads more naturally than "cruds".
"There were several different kinds of cruds clogging the filter after the flood."
"Crud" began as American military slang in the First World War — soldiers used it for an unidentified illness before it drifted into everyday speech as a name for any disgusting gunk.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of crud
"Crud" emerged as American slang in the early twentieth century, notably among First World War soldiers, who used it to mean an unspecified illness or ailment. Over time it broadened to denote any unpleasant, dirty, or unidentifiable substance, becoming the dominant sense today. Some dictionaries link it loosely to the Latin "crudus", meaning raw or undigested, the same root behind "crude" — but the precise path by which the modern noun arose is not securely documented, so details of its earliest attestation are best stated only generally.
How crud is actually used
Register is firmly informal — "crud" belongs to casual conversation rather than formal or technical writing, where terms like "residue", "sediment", or "contaminant" are preferred. Its tone is mildly comic or dismissive, often applied to substances too unappealing or trivial to identify precisely. The medical sense is chiefly American and somewhat dated, though "feeling like crud" remains current colloquially.
Easily confused with crud
"Curd" is the thickened, coagulated part of milk used to make cheese and desserts, while "crud" is informal slang for any unpleasant dirt or residue.