Topmost means highest of all. The topmost branch, the topmost shelf, topmost of the pile.
It is a double superlative, since top is already the highest, and English keeps a handful of these — uppermost, innermost, utmost. It is slightly formal and always goes before the noun rather than after the verb.
1adjectivetopmostHighest of all.
“The cat climbed to the topmost branch and then refused to come down.”
topmost is a position.
Proto-Germanic
*tuppaz — braid, pigtail, end
Proto-West Germanic
*topp
Old English
topp — top, highest part; summit; crest; tassel, tuft; (spinning) top, ball; a tuft or ball at the highest point of anything
Middle English
top
English
top
English, today
topmost
From top + -most. top comes from Middle English top, toppe, from Old English topp (“top, highest part; summit; crest; tassel, tuft; (spinning) top, ball; a tuft or ball at the highest point of anything”), from Proto-West Germanic topp, from Proto-Germanic tuppaz (“braid, pigtail, end”), of unknown ultimate origin. Compare typologically apex (<< h₂ep- (“to join, attach, fasten, fit”)). Cognate with stq Top (“top”), cim sòpf (“braid”), Dutch top (“top, summit, peak”), German Topp (“top of a mast”), {{m|de|
Etymology from Wiktionary, CC BY-SA