Skinny vermin almost entirely squashed by upstanding cardinal (6)
I believe the answer is:
dermic
'skinny' is the definition.
(thesaurus)
'vermin almost entirely squashed by upstanding cardinal' is the wordplay.
'vermin' becomes 'mice'.
'almost entirely' means to remove the last letter.
'squashed by' means one lot of letters go next to another.
'upstanding' is a reversal indicator.
'cardinal' becomes 'red' (I've seen this in other clues**).
'red' in reverse letter order is 'der'.
'mice' with its final letter taken away is 'mic'.
'mic' after 'der' is 'DERMIC'.
(Another definition for dermic that I've seen is " Relating to skin".)