Specious argument deviously stops him wasting time (7)
I believe the answer is:
sophism
'specious argument' is the definition.
(I've seen this before)
'deviously stops him wasting time' is the wordplay.
I cannot really understand how this works, but
'him' could be 'hi' and 'hi' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sophism that I've seen before include "specious argument" , "False argument" , "faulty reasoning" .)