Slender and small, not weighing much (6)
I believe the answer is:
slight
'slender' is the definition.
(synonyms)
'small not weighing much' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'not weighing much' becomes 'light' (I've seen this in another clue).
's'+'light'='SLIGHT'
'and' is the link.
(Other definitions for slight that I've seen before include "Flimsy, tenuous" , "Minor - insult" , "Small in degree; insult" , "Redeemer" , "Minor -- snub" .)