Diminish
late Middle English: blend of archaic minish ‘diminish’ (based on Latin minutia ‘smallness’) and obsolete diminue ‘speak disparagingly’ (based on Latin deminuere ‘lessen’ (in late Latin diminuere ), from minuere ‘make small’).
wiktionary
Formed under the influence of both diminue (from Old French diminuer, from Latin dīminuo) and minish.
etymonline
diminish (v.)
early 15c., diminishen, "to lessen, make or seem to make smaller," from merger of two obsolete verbs, diminue and minish.
Diminue (late 14c.) is from Old French diminuer "make small," from Latin diminuere "break into small pieces," variant of deminuere "lessen, diminish," from de- "completely" (see de-) + minuere "make small" (from PIE root *mei- (2) "small"). Minish (mid-14c.) is from Old French menuisier, from Latin minuere.
Meaning "to lower in power, importance, or estimation" is from mid-15c. Intransitive sense of "to grow less, become or appear smaller" is from 1510s. Related: Diminishes; diminishing.
