toast (v.1)

"to brown with heat," late 14c., from Old French toster "to toast, to grill, roast, burn" (12c.), from Vulgar Latin *tostare (source of Italian tostare, Spanish tostar), frequentative of Latin torrere (past participle tostus) "to parch," from PIE root *ters- "to dry." Related: Toasted; toasting.

toast (n.1)

"piece of bread browned by fire or dry heat," early 15c., from toast (v.1); originally as something added to wine, ale, etc. From 17c. in the modern sense as something eaten on its own with a spread. Slang meaning "a goner, person or thing already doomed or destroyed" is recorded by 1987, perhaps from notion of computer circuits being "fried," and with unconscious echoes of earlier figurative phrase to be had on toast (1886) "to be served up for eating." But other sources claim the extended sense and popularity is from the 1984 film "Ghostbusters."

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. 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 in which her health was drunk.

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.

toast (v.2)

"to propose or drink a toast," 1700, from toast (n.2). This probably is the source of the Jamaican and African-American vernacular word meaning "extemporaneous narrative poem or rap" (1962). Related: Toasted; toasting.

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Definitions of toast from WordNet
toast (n.)
slices of bread that have been toasted;
toast (n.)
a celebrity who receives much acclaim and attention;
he was the toast of the town
toast (n.)
a person in desperate straits; someone doomed;
one mistake and you're toast
Synonyms: goner
toast (n.)
a drink in honor of or to the health of a person or event;
Synonyms: pledge
toast (v.)
make brown and crisp by heating;
toast bread
Synonyms: crispen / crisp
toast (v.)
propose a toast to;
Let us toast the birthday girl!
Synonyms: drink / pledge / salute / wassail