underreaction

un·der·re·act

U0056600 (ŭn′dər-rē-ăkt′)intr.v. un·der·re·act·ed, un·der·re·act·ing, un·der·re·acts To react with insufficient enthusiasm, force, or emphasis.
un′der·re·ac′tion n.

underreaction

(ˌʌndərɪˈækʃən) na less intense reaction than is expected or appropriate