Chap, if elderly, having various functions (8)
I believe the answer is:
manifold
'having various functions' is the definition.
(having multiple forms or functions)
'chap if elderly' is the wordplay.
'chap' becomes 'Man' (chap can mean a man).
'elderly' becomes 'old' (similar in meaning).
'man'+'if'+'old'='MANIFOLD'
(Other definitions for manifold that I've seen before include "In various ways" , "of numerous parts" , "car part?" , "having several different forms?" , "Many and various" .)