EnglishMain Dictionary
therein
Universal Words
adverb
(formal or law) in the place, object, document, etc. mentioned:
The insurance policy covers the building and any fixtures contained therein. * In court she denied any knowledge of the article and the allegations made therein.
IDIOMS
therein lies... used to emphasize the result or CONSEQUENCE of a particular situation:
He works extremely hard and therein lies the key to his success.