1560s, "full of dreams," hence "associated with dreams," from dream (n.) + -y (2). Sense of "dream-like, vague, indistinct" is by 1848. Meaning "perfect, ideal," is noted as a teen vogue word in 1941, American English teen slang. Compare dreamboat "romantically desirable person;" dream girl, etc. Related: Dreamily; dreaminess.
before vowels oneir-, word-forming element meaning "of or pertaining to a dream or dreams," from Greek oneiros "a dream," a word of uncertain origin, perhaps related to Armenian anurj, Albanian (Gheg) âdërrë.
"romantically desirable person," 1947, from dream (n.) + boat (n.). The phrase was in use about two decades before that. "When My Dream Boat Comes Home" was the title of a 1936 song credited to Guy Lombardo and "Dream Boat" was the title of a 1929 book.
It is rare indeed that a designer ever has the opportunity to build his dream boat. Chris Smith, all his life, had held in mind a boat of about fifty feet overall which would be the last word in yacht design and performance. [Motor Boating, December 1929]