It's a measure of what's left for Ghent movement (6)
I believe the answer is:
length
'it's a measure' is the definition.
(length is a kind of measure)
'what's left for ghent movement' is the wordplay.
'what's left' becomes 'l' (common abbreviation).
'for' means one lot of letters go next to another.
'movement' is an anagram indicator.
'ghent' is an anagram of 'ength'.
'l'+'ength'='LENGTH'
'of' is the link.
(Other definitions for length that I've seen before include "Object's longest dimension" , "Duration or distance" , "Measure of distance, end to end" , "A brief swim" , "Measure (to which one should bowl?)" .)