IPA: /ˈʌndərˌjuːz/
KK: /ˈʌndərˌjus/
To use something less than what is needed or expected.
Many people underuse their vacation days, missing out on valuable time off.
Past: underused
Past Participle: underused
Underuse → It is formed from "under-" (meaning below or insufficiently) and "use" (from Old French *user*, meaning to employ or utilize). The word "underuse" means to use something insufficiently or not to its full potential.
Think of using something 'insufficiently' ('under-') — that's why underuse means not using something enough.