westernmost (adj.)

"toward or of the west," late Old English westerne "western, westerly, coming from the west," from west + -erne, suffix denoting direction. The noun meaning "book or movie about the Old West" is first attested 1909. Westerner is from 1837 as "person from the U.S. West," 1880 as "Euro-American," as opposed to Oriental.

superlative suffix of adjectives and adverbs, Middle English alteration (by influence of unrelated most) of Old English -mest, a double superlative, from -mo, -ma (cognate with Latin -mus; compare Old English forma "first," meduma "midmost") + superlative ending -est. Now generally mistaken as a suffixal form of most.