Optimum
late 19th century: from Latin, neuter (used as a noun) of optimus ‘best’.
wiktionary
From New Latin, neuter of Latin optimus(“best, very good”), from the root or in ops(“work”), omnis(“all”).
etymonline
optimum (n.)
1879, from Latin optimum, neuter singular of optimus "best, very good" (used as a superlative of bonus "good"), perhaps (Watkins) related to ops "power, resources" (in which case the evolution is from "richest" to "the most esteemed," thus from PIE root *op- "to work, produce in abundance"); or perhaps it is related to ob "in front of" (de Vaan), with superlative suffix *-tumos.
In English the word was used originally in biology, in reference to "conditions most favorable" (for growth, metabolic processes, etc.). As an adjective, "best or most favorable," from 1885.
