I was looking through Ivan Shmelyov‘s Лето Господне [Leto Gospodne, The summer/year of the Lord], a loving reconstruction of the religious and folk life of prerevolutionary Russia, when my eye hit on the unusual word ефимоны [efimóny]. Curious, I looked it up in Vasmer (who has it as ефимон, even though it seems always to be used in the plural), and discovered it meant “great penitential psalm of Andrew of Crete read at the evening service in the first week of Great Lent,” the Old Russian form was мефимонъ [mefimon], and the etymology — wait for it — is from Greek μεθ’ἡμῶν ‘with us [is God]’! Isn’t that great?
And just above it was an equally obscure word with an equally wonderful etymology, ефимок [efímok], a name for an old coin, which comes (via Polish joachymik < Latin Joachimicus) from Joachimsthal (now Czech Jáchymov); to quote Wikipedia, “The Joachimsthaler coins minted there in the 16th century became known as thaler for short, with the word ‘dollar’ and similar words for monetary units in many languages deriving from it.” So ефимок and dollar are twins, coming from different ends of Joachim’s Valley!
Unrelated, but as a public service announcement: there’s a Kickstarter campaign for an effort to “write, illustrate and publish four books in the endangered languages of indigenous cultures in the Chittagong Hill Tracts region”; if that is of interest to you, check out the link.