Metrical measures - or not metrical measures (4)
I believe the answer is:
feet
'measures' is the definition.
(I know this)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for feet that I've seen before include "Old measures - that fill shoes" , "Lower extremities" , "Imperial units of length" , "Have both on the ground to be practical" , "Three of these in yard" .)