Roget's 21st Century Thesaurus, Third Edition Copyright © 2013 by the Philip Lief Group.

WORD ORIGIN

1610s, originally in the figurative sense, of feelings, conditions, etc., from un- (1) "not" + fathomable. Literal sense attested from 1670s. Related: Unfathomably.

Roget's 21st Century Thesaurus, Third Edition Copyright © 2013 by the Philip Lief Group.