Generally considered to be a compound of onomatopoeia ぼ (bo) + adverbial particle と (to). Extension of shorter version ぼっと (botto), emphasizing an extended ongoing state of mental or visual fuzziness, vagueness, or indistinctness.
ぼうっと (rōmaji bōtto)
- Unclearly, indistinctly, vaguely.
- The sound of a fire burning strongly.
- By extension, indicating that someone's face is flushing red: blushingly.