Focus on small vessel coming in (9)
I believe the answer is:
spotlight
'focus' is the definition.
(I've seen this before)
'small vessel coming in' is the wordplay.
'small' becomes 'slight' (I've seen this before).
'vessel' becomes 'pot' (pot is a kind of vessel).
'coming in' indicates putting letters inside.
'slight' placed around 'pot' is 'SPOTLIGHT'.
'on' is the link.
(Other definitions for spotlight that I've seen before include "Beam directed on small area or on stage performer" , "Focus" , "Give prominence to" , "fame" , "Lit up in public here" .)