Lenient
mid 17th century (in lenient (sense 2)): from Latin lenient- ‘soothing’, from the verb lenire, from lenis ‘mild, gentle’.
wiktionary
From Middle French lénient, from Latin lēniens, present participle of lēnīre(“to soften, soothe”), from lēnis(“soft”).
etymonline
lenient (adj.)
1650s, "relaxing, soothing" (a sense now archaic), from French lenient, from Latin lenientem (nominative leniens), present participle of lenire "to soften, alleviate, allay; calm, soothe, pacify," from lenis "mild, gentle, calm," which probably is from a suffixed form of PIE root *lē- "to let go, slacken."
The usual modern sense of "mild, merciful" (of persons or actions) is first recorded 1787. In earlier use was lenitive, attested from early 15c. of medicines, 1610s of persons. Related: Leniently.
