Definition of plain-hearted in US English:

plain-hearted

adjective

rare
  • Sincere and open; without deceit or guile; ingenuous, innocent.

Origin

Early 17th century; earliest use found in John Deacon (fl. 1585–1616). From plain + hearted.

Pronunciation

plain-hearted

/ˌpleɪnˈhɑːtɪd/