Definition of heart-in-mouth in US English:

heart-in-mouth

adjective

  • That causes great apprehension or alarm; anxious; thrilling. Compare to have one's heart in one's mouth.

adverb

  • Usually without hyphens. Anxiously; apprehensively; with trepidation.

Origin

Early 19th century (in an earlier sense). From heart + in + mouth.

Pronunciation

heart-in-mouth

/ˌhɑːtɪnˈmaʊθ/