Furthest to the east; the most eastern in position or location.
Compound of 'east' + 'most' (superlative suffix, from Old English 'mæst'). Similar to 'topmost' or 'westmost,' it expresses the extreme degree of a directional quality.
Superlatives with compass directions are less common in modern English than they were historically—we say 'easternmost' more often now, but 'eastmost' shows how English once preferred different word endings that are now archaic.
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