Height of a large bird due to be moved (8)
I believe the answer is:
altitude
'height' is the definition.
(synonyms)
'a large bird due to be moved' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'bird' becomes 'tit' (tit is a kind of bird).
'to be moved' indicates anagramming the letters.
'due' with letters rearranged gives 'ude'.
'a'+'l'+'tit'+'ude'='ALTITUDE'
'of' acts as a link.
(Other definitions for altitude that I've seen before include "Height, elevation" , "Height (above ground)" , "Height above the earth's surface" , "Loftiness" , "Height above sea level" .)