Epic dream could be "Live for the moment" (5,4)
I believe the answer is:
carpe diem
'live for the moment' is the definition.
('carpe diem' is Latin for 'seize the day')
'epic dream could be' is the wordplay.
'could be' is an anagram indicator.
'epic'+'dream'='epicdream'
'epicdream' is an anagram of 'CARPE DIEM'.
(Other definitions for carpe diem that I've seen before include "Enjoy the moment! (Latin)" , "from Horace" , "Gather ye rosebuds" , "make the most of today" , "'Seize the day'" .)