mirabile dictu interj.

c. 1300, merivelle, "a miracle; a thing, act, or event which causes astonishment," also "wonderful story or legend," from Old French merveille "a wonder, surprise, miracle," from Vulgar Latin *miribilia (source also of Spanish maravilla, Portuguese maravilha, Italian maraviglia), altered from Latin mirabilia "wonderful things," from noun use of neuter plural of mirabilis "wonderful, marvelous, extraordinary; strange, singular," from mirari "to wonder at," from mirus "wonderful" (see smile (v.)). A neuter plural treated in Vulgar Latin as a feminine singular. Related: Marvels. The Marvel comics brand dates to 1961.

Proto-Indo-European root meaning "to show," also "pronounce solemnly," "also in derivatives referring to the directing of words or objects" [Watkins].

It forms all or part of: abdicate; abdication; addict; adjudge; apodictic; avenge; benediction; betoken; condition; contradict; contradiction; dedicate; deictic; deixis; dictate; diction; dictionary; dictum; digit; disk; ditto; ditty; edict; Eurydice; index; indicate; indication; indict; indiction; indictive; indite; interdict; judge; judicial; juridical; jurisdiction; malediction; malison; paradigm; policy (n.2) "written insurance agreement;" preach; predicament; predicate; predict; prejudice; revenge; soi-disant; syndic; teach; tetchy; theodicy; toe; token; valediction; vendetta; verdict; veridical; vindicate; vindication; voir dire.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit dic- "point out, show;" Greek deiknynai "to show, to prove," dike "custom, usage;" Latin dicere "speak, tell, say," digitus "finger," Old High German zeigon, German zeigen "to show," Old English teon "to accuse," tæcan "to teach."