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Webster 1913 Edition

Adj.

Most distant; farthest.

A spacious cave within its

farmost

part.

Dryden.

Adj.

[far and most.] Most distant or remote.

farmost ‎(not comparable)

(obsolete) Most distant; farthest.
- (Can we date this quote?), Dryden
  A spacious cave within its farmost part.