Origin and history of epithalamium

plural thalami, 1753, in botany, "the receptacle of a flower," Modern Latin, from Latin thalamus "inner chamber, sleeping room, the women's apartment" (hence, figuratively, "marriage, wedlock"), from Greek thalamos "inner chamber, bedroom," related to thalame "den, lair," tholos "vault, vaulted building." Also used in English in anatomy since 1756 in reference to a part of the forebrain where a nerve appears to originate.

before vowels reduced to ep-, before aspirated vowels eph-, word-forming element meaning "on, upon, above," also "in addition to; toward, among," from Greek epi "upon, at, close upon (in space or time), on the occasion of, in addition," also "after," from PIE *epi, *opi "near, at, against" (source also of Sanskrit api "also, besides;" Avestan aipi "also, to, toward;" Armenian ev "also, and;" Latin ob "toward, against, in the way of;" Oscan op, Greek opi- "behind;" Hittite appizzis "younger;" Lithuanian ap- "about, near;" Old Church Slavonic ob "on"). A productive prefix in Greek; also used in modern scientific compounds (such as epicenter).