tonight

noun

1. this present or coming night; the night of this present day.

adverb

2. on this present night; on the night of this present day.
3. Obsolete. during last night.

noun

1. the night or evening of this present day

adverb

2. in or during the night or evening of this day
3. archaic last night

Old English toniht “tomorrow night” (Anglo-Saxon day began at sunset), from to “at, on” (see to) + niht (see night). Written as two words until 18c., after which it was to-night until early 20c.