Imagine, concoct (5,2)
I believe the answer is:
dream up
I believe this is a double definition.
'imagine' is the first definition.
(I've seen this before)
'concoct' is the second definition.
(synonyms)
(Other definitions for dream up that I've seen before include "Invent (something)" , "Imagine, invent" , "Invent through imagination" , "'Devise or invent (5,2)'" , "Concoct" .)