3 last seen in coat pocket (4)
I believe the answer is:
twee
'3' is the definition.
Both the definition and answer are adjectives. Maybe you can see a link between them that I can't see?
'last seen in coat pocket' is the wordplay.
'last' becomes 't' (I've seen this in other clues).
'seen in coat pocket' becomes 'wee' (I can't justify this - if you can you should believe this answer much more).
't'+'wee'='TWEE'
Can you help me to learn more?
(Other definitions for twee that I've seen before include "Overly sentimental or pretty" , "Excessively cute" , "Affectedly sweet" , "Overly cute" , "Small and sweet (colloq.)" .)