Seeming to be less 'in' somehow (10)
I believe the answer is:
ostensible
'seeming' is the definition.
('ostensible' can be a synonym of 'seeming')
'to be less in somehow' is the wordplay.
'somehow' indicates anagramming the letters.
'to'+'be'+'less'+'in'='tobelessin'
'tobelessin' is an anagram of 'OSTENSIBLE'.
(Other definitions for ostensible that I've seen before include "Apparent" , "Supposed" , "Seeming" , "Manifest" , "Apparently true" .)