Number touching part of joint (5)
I believe the answer is:
tenon
'part of joint' is the definition.
(I've seen this before)
'number touching' is the wordplay.
'number' becomes 'ten' (ten is a kind of whole number).
'touching' becomes 'on'.
'ten'+'on'='TENON'
(Other definitions for tenon that I've seen before include "One projecting" , "Nonet (anag.)" , "Joint - tonne (anag)" , "piece of carpentry?" , "Part of a wooden joint" .)