A huge order for tar? (5)
I believe the answer is:
avast
'order for tar?' is the definition.
(I've seen this before)
'a huge' is the wordplay.
'huge' becomes 'vast' (I've seen this in another clue).
'a'+'vast'='AVAST'
(Other definitions for avast that I've seen before include "Stop (nautical)" , "Stop, nautically speaking" , "Stop! (naut.)" , ""stop" signal" , "Stop on board" .)