word-forming element, in modern use meaning "good, well," from Greek eus "good," eu "well" (adv.), also "luckily, happily" (opposed to kakos), as a noun, "the right, the good cause," from PIE *(e)su- "good" (source also of Sanskrit su- "good," Avestan hu- "good"), originally a suffixed form of root *es- "to be." In compounds the Greek word had more a sense of "greatness, abundance, prosperity," and was opposed to dys-.

"scientific study of death," 1837, from thanato- "death" + -logy. In 1970s, some undertakers made a bid to be called thanatologists; but from 1974 that word has been used principally in reference to specialists in the needs of the terminally ill.

word-forming element in names of countries, diseases, and flowers, from Latin and Greek -ia, noun ending, in Greek especially used in forming abstract nouns (typically of feminine gender); see -a (1). The classical suffix in its usual evolution (via French -ie) comes to Modern English as -y (as in familia/family, also -logy, -graphy). Compare -cy.

In paraphernalia, Mammalia, regalia, etc. it represents Latin or Greek -a (see -a (2)), plural suffix of nouns in -ium (Latin) or -ion (Greek), with formative or euphonic -i-.

Proto-Indo-European root meaning "to be."

It forms all or part of: absence; absent; am; Bodhisattva; entity; essence; essential; essive; eu-; eucalyptus; Eucharist; Euclidean; Eudora; Eugene; eugenics; eulogy; Eunice; euphemism; euphoria; euthanasia; homoiousian; improve; interest; is; onto-; Parousia; present (adj.) "existing at the time;" present (n.2) "what is offered or given as a gift;" proud; quintessence; represent; satyagraha; sin; sooth; soothe; suttee; swastika; yes.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit asmi, Hittite eimi, Greek esti-, Latin est, Old Church Slavonic jesmi, Lithuanian esmi, Gothic imi, Old English eom, German ist.

by 1915, in place of earlier and etymologically correct euthanatize (1873); see euthanasia + -ize. Related: Euthanized; euthanizing.