"last syllable but one of a word or verse, a penult," 1580s, from Latin pænultima (syllaba), "the next to the last syllable of a word or verse," from fem. of Latin adjective pænultimus "next-to-last," from pæne "almost" (a word of uncertain origin) + ultimus "final" (see ultimate).
1590s (implied in proximately), "closely neighboring; next, immediate, without intervention of a third," from Late Latin proximatus, past participle of proximare "to draw near, approach," from proximus "nearest, next; most direct; adjoining," figuratively "latest, most recent; next, following; most faithful," superlative of prope "near" (see propinquity). Meaning "coming next in a chain of causation" is by 1660s. Related: Proximately.
<a href="https://www.etymonline.com/word/penultimate">Etymology of penultimate by etymonline</a>
Harper, D. (n.d.). Etymology of penultimate. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/penultimate