I . n.
Revery, fancy, fantasy, conceit, illusion, delusion, vagary, idle fancy, day-~, castle in the air, château en Espagne .
II . v. n.
Have visions in sleep.
Think, imagine, fancy, have a notion.
Give a loose rein to the fancy, give the reins to the imagination, indulge in revery, build castles in the air.