Spanish agreement to adopt multi-variable incentives (7)
I believe the answer is:
stimuli
'incentives' is the definition.
(I've seen this before)
'spanish agreement to adopt multi-variable' is the wordplay.
'spanish agreement' becomes 'si' (Spanish for yes).
'to adopt' indicates putting letters inside.
'variable' indicates an anagram.
'multi' is an anagram of 'timul'.
'si' enclosing 'timul' is 'STIMULI'.
(Other definitions for stimuli that I've seen before include "Things that produce a response" , "Incentives, spurs" , "Things that rouse one to activity" , "Jogs" , "Things promoting activity" .)