Frank is a little unrealistic and idealistic (6)
I believe the answer is:
candid
'frank' is the definition.
(synonyms)
'a little unrealistic and idealistic' is the wordplay.
'a little' indicates the answer is hidden within the clue (a little bit of the clue).
'CANDID' is hidden within 'unrealistic and idealistic'.
'is' is the link.
(Other definitions for candid that I've seen before include "Very clear" , "Free and frank" , "Blunt; frank" , "Impartial" , "Frank - open" .)