Etymology
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au fait (adj.)

1743, French, "to the point, to the matter under discussion," literally "to the fact," from au "to the" (see au) + fait "fact" (see feat). Used in French with sense of "acquainted with the facts, expert, fully skilled."

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maitre d'hotel 

1530s, "head domestic, master or superintendent of the table in a mansion," from French maître d'hôtel, literally "house-master," from Old French maistre "master; skilled worker, educator" (12c.), from Latin magistrum (see magistrate). Sense of "hotel manager, manager of a dining room" is from 1890. Shortened form maître d' is attested from 1942; simple maitre in this sense is from 1899.

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hot dog (n.)

also hotdog, "sausage on a split roll," c. 1890, American English, from hot (adj.) + dog (n.). Many early references are in college student publications; later popularized, but probably not coined, by cartoonist T.A. "Tad" Dorgan (1877-1929). It is said in early explanations to echo a suspicion (occasionally justified) that sausages contained dog meat.

Meaning "someone particularly skilled or excellent" (with overtones of showing off) is from 1896. Connection between the two senses, if any, is unclear. Hot dog! as an exclamation of approval was in use by 1906.

hot-dog, n. 1. One very proficient in certain things. 2. A hot sausage. 3. A hard student. 4. A conceited person. ["College Words and Phrases," in Dialect Notes, 1900]

Related: Hot-dogger; hot-dogging.

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