What it means
A daydreamer is the one whose mind is forever drifting off somewhere lovelier than the meeting they're sitting in, staring out the window, building castles in the air, missing their name being called twice. It's not laziness, just a head full of wandering thoughts and quiet what-ifs. Said fondly, often of the creative, slightly absent-minded type.
Usage examples
"She's a born daydreamer, half her notebooks are doodles and little stories."
"Sorry, I drifted off, total daydreamer when a meeting runs long."
"He's such a daydreamer, asked him to pass the salt and he was halfway off designing his future treehouse."
"Our kid's a proper daydreamer, always gazing out the car window like he's in his own film."
Where it comes from
"Daydreamer" is built from "daydream" plus the everyday "-er" ending for a person who does the thing. "Daydream" has been in English since the 19th century for dreaming while awake, and "daydreamer" followed naturally for someone who drifts off into those bright little mind-movies.
