IPA: //nɒnˈswɪmə//
KK: /nɑnˈswɪmər/
A person who does not know how to swim or is unable to swim.
At the beach, I noticed a few nonswimmers who were hesitant to enter the water.
Nonswimmer is formed from "non-" (meaning not) and "swimmer" (from Old English "swimman", meaning to swim). The word describes a person who does not swim.
Think of 'not' ('non-') being added to 'swimmer' — this helps you remember that a nonswimmer is someone who does not swim.