A measure of 45 inches (3)
I believe the answer is:
ell
'a measure of 45 inches' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ell that I've seen before include "Former measure of length" , "Former textile measure" , "Old measure of length about 45 inches" , "Embellish with old measure of length" , "Measure, approx. fourty-five in." .)