Critically examine small tin (4)
I believe the answer is:
scan
'critically examine' is the definition.
'scan' can be an answer for 'examine' (scanning is a kind of examining). I'm unsure of the 'critically' bit.
'small tin' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'tin' becomes 'can' (synonyms).
's'+'can'='SCAN'
Can you help me to learn more?
(Other definitions for scan that I've seen before include "Read hastily" , "at one's feet?" , "show in this?" , "Cast an eye over" , "Analyse a piece of verse for metre" .)