Very thin (5)
(Other definitions for weedy that I've seen before include "Thin, puny (colloq.)" , "wimpish" , "Scraggy" , "Underdeveloped" , "quite unlike Charles Atlas" .)
'very thin' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for skinny that I've seen before include "Lacking food" , "Of person, very thin" , "Spare: coffee with skimmed milk" , "Lean" , "Pejoratively thin" .)