The term 'build castles in the air' is an idiom that means to have unrealistic expectations or to plan something that is impossible to achieve. The crossword solutions for this term are 'dreamed' (7 letters), 'DREAMING' (8 letters), 'ROOKS' (5 letters) and 'DAYDREAMS' (9 letters). Dreamed and DREAMING refer to having a vision or imagining something, while ROOKS and DAYDREAMS refer to the idea of fantasizing or having a fanciful notion. All of these words together suggest that someone is indulging in unrealistic hopes and ambitions.