Key tip joining variable fabric (6)
I believe the answer is:
chintz
'fabric' is the definition.
(I know that chintz is a type of fabric)
'key tip joining variable' is the wordplay.
'key' becomes 'c' (musical key).
'tip' becomes 'hint' (synonyms).
'joining' is a charade indicator (letters next to each other).
'variable' becomes 'z' (algebra).
'c'+'hint'+'z'='CHINTZ'
(Other definitions for chintz that I've seen before include "Glazed cotton print" , "Printed material used for, eg., upholstery" , "Brightly printed cotton fabric" , "'Cotton fabric, often used for curtains or upholstery (6)'" , "Printed multi-coloured cotton fabric" .)