IPA: /ˌʌndərˈrɛkt/
KK: /ʌndərˈrɛkt/
To respond to a situation or event with less emotion or intensity than is expected or appropriate.
She tended to underreact to stressful situations, which sometimes worried her friends.
Past: underreacted
Past Participle: underreacted
Underreact → It is formed from "under-" (meaning below or insufficiently) and "react" (from Latin "reactare", meaning to act in response). The word "underreact" means to respond insufficiently or inadequately to a situation.
Think of responding 'insufficiently' ('under-') to something that requires a reaction ('react').