Discover, as an idea (3,2)
'discover as an idea' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hit on that I've seen before include "Make advances to (US)" , "Discovered suddenly or, in modern slang, made advances towards" , "Try to get off with" , "Serendipitously find" , "try a pass?" .)