Gather fellow gets elderly (4)
I believe the answer is:
fold
'gather' is the definition.
(thesaurus)
'fellow gets elderly' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'gets' means one lot of letters go next to another.
'elderly' becomes 'old' ('old' can be similar in meaning to 'elderly').
'f'+'old'='FOLD'
(Other definitions for fold that I've seen before include "enclosure" , "Prepare pages to put in small envelope" , "Pleat; sheep pen" , "close" , "Gather < church" .)