Devout old maid perhaps clutching book (9)
I believe the answer is:
observant
'devout' is the definition.
(thesaurus)
'old maid perhaps clutching book' is the wordplay.
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'maid perhaps' becomes 'servant' (maid is a kind of servant).
'clutching' means one lot of letters goes inside another.
'book' becomes 'b' (abbreviation for book).
'o'+'servant'='oservant'
'oservant' placed around 'b' is 'OBSERVANT'.
(Other definitions for observant that I've seen before include "Heedful" , "taking things in" , "Quick to notice things" , "diligent in duty" , "Quick at noticing things, attentive" .)