Etymology
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sanitarium (n.)

1829, "an improper form for sanatorium" [Century Dictionary], meant to indicate "place dedicated to health," perhaps based on sanitary or from Latin sanitas "health," from sanus "healthy; sane" (see sane).

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convalescence (n.)

"a gradual recovery of strength and health after a sickness," late 15c., from French convalescence (15c.), from Late Latin convalescentia "a regaining of health," from convalescentem (nominative convalescens), present participle of Latin convalescere"thrive, regain health, begin to grow strong or well," from assimilated form of com-, here perhaps an intensive prefix (see com-), + valescere "to begin to grow strong," inchoative of valere "to be strong" (from PIE root *wal- "to be strong"). Related: Convalescency.

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biohazard (n.)
also bio-hazard, "organic material that carries a significant health risk," 1973, from bio- + hazard (n.).
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gesundheit (interj.)

1914, from German Gesundheit, literally "health!", from Old High German gisunt, gisunti "healthy" (see sound (adj.)). Also in the German toast auf ihre Gesundheit "to your health." God bless you after someone sneezes is credited to St. Gregory the Great, but the pagan Romans (Absit omen) and Greeks had similar customs.

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fluoridation (n.)
1904, "process of absorbing fluoride," from fluoride + -ation. In reference to adding traces of fluoride to drinking water as a public health policy, from 1949.
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sickish (adj.)

"indisposed, in a disordered state of health," 1580s, from sick (adj.) + -ish. Related: Sickishly.

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spa (n.)
"medicinal or mineral spring," 1620s, from the name of the health resort in eastern Belgium, known since 14c., that features mineral springs believed to have curative properties. The place name is from Walloon espa "spring, fountain." As "commercial establishment offering health and beauty treatments," 1960.
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toast (n.2)

"a call to drink to someone's health," 1690s (but said by Steele, 1709, to date to the reign of Charles II), originally referring to the beautiful or popular woman whose health is proposed and drunk to. The custom apparently has its origin in the use of spiced toast (n.1) to flavor drink; the lady being regarded as figuratively adding piquancy to the wine which was drunk to her health. 

The custom itself is much older than this word for it, and the expectation of a bit of toast in a mug of ale at a tavern is well attested in many 17c. drinking songs, though none of them seems to give a reason for it. 

Steele's story ["Tatler," No. 24] is that an (unnamed) beauty of the day was taking the cold waters at Bath, when a gentleman dipped his cup in the water and drank it to her health; another in his company wittily (or drunkenly) replied that, while he did not care for the drink, he would gladly enjoy the toast. Meaning "one whose health is proposed and drunk to" is from 1746. Toast-master attested from 1749.

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fletcherism (n.)
dietary system emphasizing very thorough mastication, 1903, from -ism + name of Horace Fletcher (1849-1919), U.S. health enthusiast. Related: Fletcherize; fletcherized.
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restorative (adj.)

"capable of restoring health or strength," late 14c., restoratif, from Old French restoratif, restauratif, from restorer (see restore) or from Medieval Latin restaurativus.

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