The most common and most likely answer to this crossword clue is the 4 letter word CANT
I've seen this crossword clue in Financial Times
C
A
N
T
More clues leading to the result CANT
- Key worker's jargon
- Is unable to swing round
- Admission of incompetence and insincerity
- Inclination / to make a lot pay?
- Insincerity not working in part of Switzerland
- Lively tune followed by tenor
- An inclination for insincerity
- Hasn’t the ability for hypocrisy
- Hypocrisy about social worker
- There’s no such word, some say – it’s slang
Buddy explains!

The straight part
We know that "slang" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case slang = cant.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CANT mean?
CANT noun- An argot, the jargon of a particular class or subgroup.
- A private or secret language used by a religious sect, gang, or other group.
- A language spoken by some Irish Travellers; Shelta.
- Empty, hypocritical talk.
- Whining speech, such as that used by beggars.
- A blazon of a coat of arms that makes a pun upon the name (or, less often, some attribute or function) of the bearer, canting arms.
- A call for bidders at a public fair; an auction.
- To speak with the jargon of a class or subgroup.
- To speak in set phrases.
- To preach in a singsong fashion, especially in a false or empty manner.
- Of a blazon, to make a pun that references the bearer of a coat of arms.
- To sell by auction, or bid at an auction.
- Side, edge, corner, niche.
- Slope, the angle at which something is set.
- A corner (of a building).
- An outer or external angle.
- An inclination from a horizontal or vertical line; a slope or bevel; a tilt.
- A movement or throw that overturns something.
- A sudden thrust, push, kick, or other impulse, producing a bias or change of direction; also, the bias or turn so given.
- (coopering) A segment forming a side piece in the head of a cask.
- A segment of the rim of a wooden cogwheel.
- A piece of wood laid upon the deck of a vessel to support the bulkheads.
- To set (something) at an angle.
- To give a sudden turn or new direction to.
- To bevel an edge or corner.
- To overturn so that the contents are emptied.
- A parcel, a division.
- To divide or parcel out.
- Lively, lusty.