Covering of slate on a dam (6)
I believe the answer is:
'covering' is the definition.
(panama is a kind of covering)
'slate on a dam' is the wordplay.
'slate' becomes 'pan' (both can mean to criticise strongly).
'on' is a charade indicator (letters next to each other).
'dam' becomes 'ma' (dam can mean the mother of an animal).
'of' acts as a link.
(Other definitions for panama that I've seen before include "What may be seen overhead" , "isthmus" , "A great canal or a straw hat" , "Country - hat - canal - cigar" , "city" .)