Extremely thin (6)
(Other definitions for skinny that I've seen before include "not having much in the way of meat" , "Lacking food" , "little of substance?" , "Unattractively thin" , "Scraggy, scrawny" .)
'extremely thin' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for gaunt that I've seen before include "place associated with Edward III's son" , "forlorn" , "Very thin, cadaverous" , "Unhealthily thin" , "Thin and pinched" .)