Material for tank top has little diamonds on (5)
I believe the answer is:
tweed
'material' is the definition.
(tweed is a kind of material)
'tank top has little diamonds on' is the wordplay.
'top' suggests taking the first letters.
'has' says to put letters next to each other.
'little' becomes 'wee' ('wee' can be similar in meaning to 'little'**).
'diamonds' becomes 'd' (abbreviation in bridge say).
'on' says to put letters next to each other.
The initial letter of 'tank' is 't'.
't'+'wee'+'d'='TWEED'
'for' acts as a link.
(Other definitions for tweed that I've seen before include "Flower on border" , "Thick woolen fabric" , "Scottish and English river" , "Harris cloth" , "Thick woollen cloth - northern river" .)