Chap's in trouble, finding source of iron (7)
I believe the answer is:
spinach
'source of iron' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'chap's in trouble' is the wordplay.
'trouble' indicates an anagram.
'chaps'+'in'='chapsin'
'chapsin' anagrammed gives 'SPINACH'.
'finding' acts as a link.
Can you help me to learn more?
(Other definitions for spinach that I've seen before include "Popeye the Sailor's favourite vegetable" , "Vegetable plant" , "Popeye the Sailor's vegetable of choice" , "Dark green vegetable" , "Some greens" .)