Origin and history of immolate

1540s, "to sacrifice, kill as a victim," from Latin immolatus, past participle of immolare "to sacrifice, bring as an offering," hence, in a general sense, "kill, slay," originally and etymologically "to sprinkle with sacrificial meal;" from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + mola (salsa) "(sacrificial) meal," which is related to molere "to grind" (from PIE root *mele- "to crush, grind"). Related: Immolated; immolating.

The victim ( victima is used of the larger, hostia of the smaller animals) was led to the altar adorned with the sacred band of white wool ( infula) and ribands ( vittae); the horns were sometimes gilded. As in the Greek rule, the victim must come willingly. Then followed the immolatio, also a counterpart of the Greek ritual, which consisted in dedicating the animal by strewing on its head the mola salsa or prepared cake (perhaps also called fertum) with wine and incense, and with the words macte esto hoc ture et hoc vino. The beast was then slain .... [Cornish (ed.), "Concise Dictionary of Greek and Roman Antiquities," 1898]

In modern use often meaning self-immolation (a phrase attested by 1779), "self-sacrifice," as distinguished from self-murder (suicide).

That acts of suicide were common among the general population of Rome, is not so certain as that self immolation was prescribed to every noble soul, in every instance where the country could be benefited by it. Examples of heroic devotedness occur in every page of Roman history. [Richard Chenevix, "An Essay Upon National Character," 1832]

Especially after c. 1800 in reference to customs in British India, notably the suttee, which might have given its popular association with sacrificial death by fire.