Thumb through short tome with doubled ring binding (5)
I believe the answer is:
ovolo
'thumb' is the definition.
(both can refer to a type of architectural moulding)
'short tome with doubled ring binding' is the wordplay.
'short tome' becomes 'vol' (short for volume).
'with doubled ring' becomes 'oo' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'binding' is an insertion indicator.
'vol' put inside 'oo' is 'OVOLO'.
'through' is the link.
(Other definitions for ovolo that I've seen before include "Rounded architectural moulding" , "decorative strip" , "Convex moulding" , "Thumb" .)