A small flat is fitting (3)

I believe the answer is:

apt

'is fitting' is the definition.
(thesaurus)

'a small flat' is the wordplay.
'small flat' becomes 'pt' (I've seen this in other clues).
'a'+'pt'='APT'

(Other definitions for apt that I've seen before include "Inclined; appropriate" , "Tap (anag.)" , "Liable" , "flat" , "Suitable or likely" .)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app