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Webster 1913 Edition

Upmost

Up′mostˊ

,

Adj.

[Cf.

.]

Highest; topmost; uppermost.

Spenser. Dryden.

Webster 1828 Edition

Upmost

UP'MOST

,

Adj.

[up and most.] Highest; topmost. [Little used. We generally use uppermost.]

Definition 2024

upmost

upmost

English

Adjective

upmost

Uppermost.
- 2013, Sam Halliday, Sonic Modernity (page 70)
  But the disjuncture between addressor and addressed such scenarios emphasise was not always (or even often) upmost in users' minds […]
Misspelling of utmost.