Weight of a cart? (5)
I believe the answer is:
carat
'weight' is the definition.
(I've seen this in another clue)
'of a cart?' is the wordplay.
'of' indicates anagramming the letters (the answer comes from or 'of' the letters).
'a'+'cart'='acart'
'acart' is an anagram of 'CARAT'.
(Other definitions for carat that I've seen before include "Unit of weight used for gems" , "Gem weight unit" , "small weight" , "Unit of gem measurement" , "Unit of measurement for the proportion of gold in an alloy" .)