Good argument for increase (4)
I believe the answer is:
grow
'increase' is the definition.
(growing is a kind of increasing)
'good argument' is the wordplay.
'good' becomes 'g' (abbreviation).
'argument' becomes 'row' (I've seen this before).
'g'+'row'='GROW'
'for' is the link.
(Other definitions for grow that I've seen before include "Gain in size" , "Become bigger" , "Mature" , "Increase in size" , "Develop; increase" .)