"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.
1711 in the political sense, "the first minister of a state," a shortening of premier minister (1680s); see premier (adj.). In U.S. usage, premier formerly was applied occasionally to the Secretary of State (late 19c.).
"capable of restoring health or strength," late 14c., restoratif, from Old French restoratif, restauratif, from restorer (see restore) or from Medieval Latin restaurativus.
"a constitutional walk," 1829, probably originally among university students, and probably short for constitutional walk or exercise; from constitutional (adj.) in the "beneficial to bodily health" sense.
toast before drinking, Spanish, literally "(good) health;" attested in English by 1931. French equivalent salut is attested in English by 1921.