Most of this person's large feet (5)
I believe the answer is:
iambi
'feet' is the definition.
(plural of iamb, a type of metrical foot in poetry)
'most of this person's large' is the wordplay.
'most of' means to remove the last letter.
'this person's' becomes 'I am' ('this person' being the crossword setter).
'large' becomes 'big' (synonyms).
'iam'+'big'='iambig'
'iambig' with its final letter taken off is 'IAMBI'.
(Other definitions for iambi that I've seen before include "Poetic feet" , "Short-long metrical feet" , "Feet of two syllables (one short and one long)" , "Concierto de Aranjuez composer" , "Poetic pieces" .)