Understand me leaving overweight chap in France (6)
I believe the answer is:
fathom
'understand' is the definition.
(fathoming is a kind of understanding)
'me leaving overweight chap in france' is the wordplay.
'leaving' indicates named letters should be taken away.
'overweight' becomes 'fat' (similar in meaning).
'chap in france' becomes 'homme' ('man' in French).
'fat'+'homme'='fathomme'
'fathomme' with 'me' removed is 'FATHOM'.
(Other definitions for fathom that I've seen before include "Measure of marine depth" , "Six feet in depth; grasp" , "Discover the meaning of - six feet" , "some distance down" , "Unit of depth - comprehend it" .)