The word "westernmost" is a transparent compound formed within English from two native elements. The base "western" originates from the Old English "west," itself from the Proto-Germanic westrą, meaning the direction of the setting sun. The superlative suffix "-most" derives from the Old English "-mest," a double superlative combining the Germanic superlative -ōst- and an old superlative suffix -ma-. When combined, the literal meaning "most western" directly and logically yields the modern sense of "farthest to the west," describing the extreme geographical limit in that direction.

Structure: western (of the west) + most (superlative suffix) - western: From Old English westerne, meaning "of the west". Its functional role is as the base adjective. - most: From Old English -mest, a superlative suffix. Its functional role is to form the superlative degree of the adjective.