Singular, feline style of singing (4)
I believe the answer is:
scat
'style of singing' is the definition.
(as in jazz scatting)
'singular feline' is the wordplay.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'feline' becomes 'cat' (cat is a kind of feline).
's'+'cat'='SCAT'
(Other definitions for scat that I've seen before include "unwelcome person may hear this" , "Dropping" , "Animal droppings - small silvery fish" , "One way of singing" , "Type of jazz singing - be off!" .)