Definitions

1. adverb

used to indicate that the preceding clause or sentence is a place or situation in which something happens or exists

“She searched the entire house, but the missing item was nowhere to be found, not even therein.”

2. adverb

used to introduce a clause or phrase that provides additional information about something previously mentioned

“The new policy will apply to all employees, including those who work therein.”

3. preposition

used to indicate a relationship between a noun or pronoun and a clause or phrase that follows

“The box is located therein.”