Deliberately lose most of the argument (5)
I believe the answer is:
throw
'deliberately lose' is the definition.
(I've seen this before)
'most of the argument' is the wordplay.
'most of' means to remove the last letter.
'argument' becomes 'row' (I've seen this before).
'the' with its last letter taken off is 'th'.
'th'+'row'='THROW'
(Other definitions for throw that I've seen before include "Try not to win" , "Light cloth cover for furniture" , "Hurl; perplex" , "return from the boundary, perhaps" , "Discard" .)