Fit he may be - in a pinch (5)
I believe the answer is:
thief
'fit he may be in a pinch' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'fit he may be' is the wordplay.
'may be' indicates anagramming the letters.
'fit'+'he'='fithe'
'fithe' with letters rearranged gives 'THIEF'.
Can you help me to learn more?
(Other definitions for thief that I've seen before include "Person who steals things" , "nicker?" , "He takes" , "One's inclined to take" , "One with taking ways" .)