Insect lost heart within four weeks (4)
I believe the answer is:
moth
'insect' is the definition.
(moth is a kind of insect)
'lost heart within four weeks' is the wordplay.
I cannot really see how this works, but
'heart' could be 'h' (card game abbreviation) and 'h' is present in the answer.
The remaining letters 'mot' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for moth that I've seen before include "Fairy like 13" , "Cloth-eating insect" , "Insect drawn to flame" , "one drawn to the bright lights" , "Night flier" .)