Idealistic (7)
'idealistic' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for utopian that I've seen before include "Ideally perfect, but impracticable" , "Just perfect, as in Thomas More's ideal country" , "Just perfect as in Thomas More's fictional country" , "Citizens of Thomas More's perfect country" , "ideal but unrealistic" .)
'idealistic' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for quixotic that I've seen before include "Unworldly" , "donnish?" , "Extravagantly romantic" , "Impractically idealistic" , "Having impractical ideas" .)