Source of old gear at home (6)
I believe the answer is:
origin
'source' is the definition.
(synonyms)
'old gear at home' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'gear' becomes 'rig' (rig is a kind of gear).
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'o'+'rig'+'in'='ORIGIN'
'of' is the link.
(Other definitions for origin that I've seen before include "Source, root" , "Where one begins" , "spring" , "Place or point of beginning (6)" , "First thing" .)