Singular stuff? Beat it! (5)
I believe the answer is:
scram
'beat it' is the definition.
(I've seen this before)
'singular stuff?' is the wordplay.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'stuff?' becomes 'cram' (cramming is a kind of stuffing).
's'+'cram'='SCRAM'
(Other definitions for scram that I've seen before include "beat hasty retreat" , "Beat it, get lost, go away" , "Leave quickly" , "Slangy order to go away, beat it" , "make emergency shut-down" .)