late 14c., "clearly revealed," from Old French manifest "evident, palpable," (12c.), or directly from Latin manifestus "plainly apprehensible, clear, apparent, evident;" of offenses, "proved by direct evidence;" of offenders, "caught in the act," probably from manus "hand" (see manual) + -festus "struck" (compare second element of infest).The phrase apparently is O'Sullivan's coinage; the notion is as old as the republic.

late 14c., "to spread" (one's fame), "to show plainly," from manifest, adj. or else from Latin manifestare "to discover, disclose, betray" (see manifest, adj.). Meaning "to display by actions" is from 1560s; reflexive sense, of diseases, etc., "to reveal as in operation" is from 1808. Related: Manifested; manifesting.

"ship's cargo," 1706; see manifest, adj.. Earlier, "a public declaration" (c.1600; compare manifesto), from French manifeste, verbal noun from manifester. Earlier still in English as "a manifestation" (1560s).