Tease tribe endlessly (3)
'tease' is the definition.
'tribe endlessly' is the wordplay.
'endlessly' says to take the centre (the ends of the words are removed).
The middle of 'tribe' is 'RIB'.
(Other definitions for rib that I've seen before include "Large leaf-vein", "Tease (sl.)", "Tease; pectoral bone", "structural member", "Poke fun at the bone".)