Old English cirice, circe "church, public place of worship; Christians collectively," from West Germanic *kirika (cf. Old Saxon kirika, Old Norse kirkja, Old Frisian zerke, Middle Dutch kerke, Dutch kerk, Old High German kirihha, German Kirche), probably [see note in OED] from Greek kyriake (oikia), kyriakon doma "Lord's (house)," from kyrios "ruler, lord," from PIE root *keue- "to swell" ("swollen," hence "strong, powerful"); see cumulus. Phonetic spelling from c.1200, established by 16c. For vowel evolution, see bury. As an adjective from 1570s.
Greek kyriakon (adj.) "of the Lord" was used of houses of Christian worship since c.300, especially in the East, though it was less common in this sense than ekklesia or basilike. An example of the direct Greek-to-Germanic progress of many Christian words, via the Goths; it probably was used by West Germanic people in their pre-Christian period.
Also picked up by Slavic, probably via Germanic (e.g. Old Church Slavonic criky, Russian cerkov). Finnish kirkko, Estonian kirrik are from Scandinavian. Romance and Celtic languages use variants of Latin ecclesia (e.g. French église, 11c.).
Church-bell was in late Old English. Church-goer is from 1680s. Church key is early 14c.; slang use for "can or bottle opener" is by 1954, probably originally U.S. college student slang. Church-mouse, proverbial in many languages for its poverty, is 1731 in English.