Old unit of measurement some levellers used (3)
I believe the answer is:
ell
'old unit of measurement' is the definition.
(unit formerly used for measuring cloth)
'some levellers used' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ELL' is hidden within 'levellers used'.
(Other definitions for ell that I've seen before include "Old measurement" , "distance" , "Embellish with old measure of length" , "Old textile measure" , "Old 45-inch measure" .)