Alligator is one on soft floor covering (7)
I believe the answer is:
reptile
'alligator is one' is the definition.
'on soft floor covering' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'soft' becomes 'p' (musical abbreviation for 'piano').
'floor covering' becomes 'tile' (I've seen this in another clue).
're'+'p'+'tile'='REPTILE'
(Other definitions for reptile that I've seen before include "eg Crocodile" , "Despicable sort" , "Lizard, for example" , "Unpleasant character" , "Eg, snake, lizard, etc" .)