Apartment is suitable (3)
I believe the answer is:
apt
This clue is a double definition.
'apartment' is the first definition.
(abbreviation in property ads for example)
'suitable' is the second definition.
(I've seen this before)
'is' is the link.
(Other definitions for apt that I've seen before include "Having a tendency" , "Tap (anag.)" , "suitable for the circumstances" , "Train" , "To the point" .)