One member takes it to be a proper abbreviation (5)
I believe the answer is:
legit
'be a proper abbreviation' is the definition.
The definition suggests a singular noun which matches the answer.
'one member takes it' is the wordplay.
'one member' becomes 'leg' (member can mean a limb).
'takes' is a charade indicator (letters next to each other).
'leg'+'it'='LEGIT'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for legit that I've seen before include "Above board (abbr)" , "Lawful, in short" , "Authorised" , "ok!" , "acceptable" .)