Part of a meter (4)
I believe the answer is:
iamb
'part of a meter' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for iamb that I've seen before include "Short-long metrical foot" , "Metrical unit" , "Part of a pentameter?" , "Metrical foot of one short, one long syllables" , "Line of verse" .)