Socialist leader inflamed by last of Truss's cuts (5)

'cuts' is the definition.
(slitting is a kind of cutting)

'socialist leader inflamed by last of truss's' is the wordplay.
'leader' indicates taking the first letters.
'inflamed' becomes 'lit' (as in a lit fire).
'by' means one lot of letters go next to another.
'last of' suggests the final letters.
The initial letter of 'socialist' is 's'.
The final letter of 'trusss' is 's'.
's'+'lit'+'s'='SLITS'