Erstwhile and Olden days

Erstwhile adjective - Having been such at some previous time.

Olden days and erstwhile are semantically related In some cases you can use "Olden days" instead the word "Erstwhile" as an adverb or an adjective.

Erstwhile and olden days are semantically related in olden topic. Sometimes you can use "Erstwhile" instead the phrase "Olden days" as an adjective or an adverb, if it concerns topics such as previously in time or order.