Frequently finding fellow gripped by books on space (5)
I believe the answer is:
often
'frequently' is the definition.
('often' can be a synonym of 'frequently')
'fellow gripped by books on space' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'gripped by' indicates putting letters inside.
'books' becomes 'ot' (Old Testament).
'on' is a charade indicator (letters next to each other).
'space' becomes 'en'.
'f' inserted within 'ot' is 'oft'.
'oft'+'en'='OFTEN'
'finding' acts as a link.
(Other definitions for often that I've seen before include "Turn away" , "Frequently, at short intervals" , "Frequent" , "Repeatedly, many times" , "Commonly" .)