Increase assuming variable follows in decimal units (9)
I believe the answer is:
intensify
'increase' is the definition.
(I know that increase is the is a more specific form of the action of intensify.)
'assuming variable follows in decimal units' is the wordplay.
'assuming' is a charade indicator (letters next to each other).
'variable follows' becomes 'ify' (I can't explain this - if you can you should give a lot more credence to this answer).
'decimal units' becomes 'tens' (I've seen this in another clue).
'in'+'tens'='intens'
'ify' after 'intens' is 'INTENSIFY'.
Can you help me to learn more?
(Other definitions for intensify that I've seen before include "Make stronger" , "Fan" .)