Exploit totally and effectively (8)
I believe the answer is:
usefully
'effectively' is the definition.
(thesaurus)
'exploit totally' is the wordplay.
'exploit' becomes 'use' (use can mean to exploit).
'totally' becomes 'fully'.
'use'+'fully'='USEFULLY'
'and' acts as a link.
(Other definitions for usefully that I've seen before include "in an advantageous way" , "Advantageously" , "In a productive manner" , "in a way that's beneficial" , "To produce a benefit" .)