retch / wretch
The verb versus the noun.
Retch is a verb: to strain to vomit. Wretch is a noun: a person who is miserable or contemptible.
Examples
Use The rough crossing left half the passengers retching at the rail.
Use The old wretch cheated his own brother out of the farm.
Avoid The old retch cheated his own brother out of the farm. (Change retch to wretch.)