Waste time showing instruction to printer (4)
I believe the answer is:
stet
'instruction to printer' is the definition.
(I've seen this before)
'waste time showing' is the wordplay.
'showing' indicates the answer is hidden within the clue.
'STET' can be found hidden inside 'waste time'.
(Other definitions for stet that I've seen before include "Let it stand (in proofing)" , "Instruction to keep" , "Leave in, as text" , "Thus, leave spelling unchanged" , "(On proofs) instruction to cancel a correction" .)