Nobleman entering New York? Just about (6)
I believe the answer is:
nearly
'just about' is the definition.
('nearly' can be a synonym of 'just about')
'nobleman entering new york?' is the wordplay.
'nobleman' becomes 'earl' (earl is a kind of nobleman).
'entering' is an insertion indicator.
'new york?' becomes 'ny'.
'earl' placed into 'ny' is 'NEARLY'.
(Other definitions for nearly that I've seen before include "pretty much" , "Close" , "Noon at eleven fifty nine am" , "Almost, not quite" , "approximately" .)