wherein
1. [ adverb ] in which; where
Examples:

"the particular state wherein you reside"

2. [ adverb ] in the course or during which
Examples:

"a period wherein he did not work"

3. [ adverb ] in regard to which
Examples:

"a case wherein he took an active part"

4. [ adverb ] in what
Examples:

"wherein consists this matter?"

Similar spelling:   whereon