Foot of gigantic bird that’s legendary in the East (7)
I believe the answer is:
trochee
'foot' is the definition.
(trochee is a kind of foot)
'gigantic bird that's legendary in the east' is the wordplay.
'gigantic bird' becomes 'roc' (I've seen this before).
'that's legendary' becomes 'the' (I am not sure about this - if you are sure you should believe this answer much more).
'in' is an insertion indicator.
'the east' becomes 'E' (abbreviation).
'roc' put inside 'the' is 'troche'.
'troche'+'e'='TROCHEE'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for trochee that I've seen before include "poetic feature" , "Foot of a stressed and an unstressed syllable" , "Long-short foot in poetry" , "Long-short metrical foot" , "A foot of two syllables, long then short" .)