IPA: //ˌʌndərˈsɛkst//
KK: /ʌndərˈsɛkst/
Having a low level of sexual desire or interest.
He felt undersexed in his relationship, as he had little interest in intimacy.
Undersexed → It is formed from "under-" (meaning below or insufficient) and "sexed" (derived from "sex" which comes from Latin "sexus", meaning gender or sexual activity). The word describes a state of having insufficient sexual activity or desire.
Think of being 'below' ('under-') the normal level of sexual activity or desire, which is what 'undersexed' means.