Preferably? Very much so! (6)
I believe the answer is:
rather
'preferably?' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for rather that I've seen before include "More precisely; instead of" , "More willingly, by preference" , "Pretty" , "with more justification" , "Most certainly" .)