I sometimes see these words written interchangeably.

Problem:
The words “retch” and “wretch” are not synonyms.

Explanation:
The word “retch” — spelled R-E-T-C-H — is a verb that dates back to the mid 1500s and means to vomit when used with an object and means to make an effort to vomit when used without an object.

The verb “retch” comes from an Old Norse word that means to hawk or spit and, when spoken, sounds like hawking or spitting.

The word “wretch” — spelled W-R-E-T-C-H — is a noun that dates back to before 900 and means an unhappy person or a person of base character.

The noun “wretch” comes from the Old English word “wrecca”, which means exile and comes from the German word “Recke”, which means warrior and comes from the Old Norse word “rekkr”, which means man.

So somehow a word for “man” transformed into a word for “warrior”, which transformed into a word for “exile”, which transformed into a word that refers to an unhappy person or a person of base character.

Many readers may know the noun “wretch” from the hymn “Amazing Grace”, which includes the lyrics “Amazing Grace! How sweet the sound that saved a wretch like me …”

Solution:
To distinguish the “retch” that starts with an “r” from the “wretch” that starts with a “w”, remember that the latter is a noun by remembering that another, similar-sounding noun is “witch”, which also starts with a “w”.