Taciturn (8)

I think it could be either:

Which length description are you looking for?:

5-6

reticent

'taciturn' is the definition.
(similar in meaning)

This is all the clue.

(Other definitions for reticent that I've seen before include "Uncommunicative" , "Not revealing one's thoughts readily" , "Reserved, shy" , "Reserved, retiring" , "Disinclined to speak" .)

I've seen this clue in The Telegraph and the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.