in, into, or towards a previous place or condition, or an earlier time:
When you take the scissors, remember to put them back.
He left a note saying "Gone out. Back soon."
He went to Brazil for two years, but now he's back (= has returned).
He looked back (= looked behind him) and saw they were following him.
Looking at her old photographs brought back (= made her remember) a lot of memories.
I was woken by a thunderstorm, and I couldn't get back to sleep (= could not sleep again).
The last time we saw Lowell was back (= at an earlier time) in January.
This tradition dates back to (= to the earlier time of) the 16th century.
* An adverb is a word that modifies a verb, adjective, another adverb, determiner, noun phrase, clause, or sentence. Adverbs typically express manner, place, time, frequency, degree, level of certainty, etc., answering questions such as how?, in what way?, when?, where?, and to what extent?. This function is called the adverbial function, and may be realised by single words (adverbs) or by multi-word expressions (adverbial phrases and adverbial clauses).