say it: peh-NUHL-tuh-muht
penultimate is a noun and adjective meaning "the next to last syllable in a word". It carries 2 recorded senses.
second last
“the author inadvertently reveals the murderer in the penultimate chapter”
“the figures in the next-to-last column”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for penultimate come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.