Erstwhile is an adjective that means ‘previous’ or ‘former.’ Occasionally, it pops up as an adverb that means ‘in the past.’
Our word of the day has been around since the 16th century, but its origin is in two much older words from Old English. The word’s first syllable E-R-S-T once meant ‘earlier’ and the second part W-H-I-L-E had the same meaning as the modern word ‘while.’
An example of erstwhile as an adverb is: The local high school was erstwhile in this location before being moved about a decade ago. As an adjective an example is: Our erstwhile principal has since retired to raise ostriches in his homeland of New Zealand.