Slender man on way oddly (7)
I believe the answer is:
willowy
'slender' is the definition.
(thesaurus)
'man on way oddly' is the wordplay.
'man' becomes 'will' (short for William).
'oddly' means one should take alternating letters (letters in odd-numbered positions).
'on'+'way'='onway'
The alternating letters of 'onway' are 'owy'.
'will'+'owy'='WILLOWY'
(Other definitions for willowy that I've seen before include "Flexible" , "Like a slender person" .)