Strong in the future, say (7)
I believe the answer is:
intense
'strong' is the definition.
(similar in meaning)
'in the future say' is the wordplay.
'the future say' becomes 'tense' (future tense).
'in'+'tense'='INTENSE'
(Other definitions for intense that I've seen before include "Concentrated, deeply felt" , "Strongly-felt" , "Strong in degree or emotion" , "Set nine (anag.)" , "Deeply felt or vehement" .)