merciful UK /ˈmɜː.sɪ.fl̩/US /ˈmɝ.sɪ.fl̩/ adjective1 •Showing mercy.`Listen, Holly. Thou art a good and honest man, and I fain would spare thee; but, oh! it is so hard for woman to be merciful.' — 1886 formsmore merciful · most merciful