Croaker spent last year in a pea-souper (4)
I believe the answer is:
frog
'croaker' is the definition.
(I've seen this in another clue)
'last year in a pea-souper' is the wordplay.
'last' says to take the final letters.
'in' means one lot of letters goes inside another.
'a pea-souper' becomes 'fog' (I've seen this before).
The final letter of 'year' is 'r'.
'r' inserted within 'fog' is 'FROG'.
'spent' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for frog that I've seen before include "An amphibian; a track plate" , "fastener" , "Amphibious jumper" , "Tailless stout-bodied amphibian" , "Adult tadpole" .)