Spend (6)
'spend' is the definition.
(synonyms)
This is all the clue.
(Other definitions for use up that I've seen before include "Consume (stocks)" , "Exhaust (resources)" , "Entirely consume" , "Expend" , "Completely consume" .)
'spend' is the definition.
(investing is a kind of spending)
This is all the clue.
(Other definitions for invest that I've seen before include "as Greeks did to Troy?" , "Put money or effort into" , "Eg, buy stocks and shares" , "speculate?" , "Formally place in office" .)
'spend' is the definition.
(I know that spend is a more specific form of pay)
This is all the clue.
(Other definitions for pay that I've seen before include "Remuneration" , "Hand over money for" , "Settle up" , "Reward for work" , "Earnings" .)