köken: From Middle High German ahtunge (“consideration, appreciation”), from Old High German ahtunga, from Proto-West Germanic *ahtungu. By surface analysis, achten + -ung. Compare Yiddish אַכטונג (akhtung), Alemannic German Achtig.
köken: Inherited from Vulgar Latin *cova, from covus, alternative form of Latin cavus (or from a variant of Late Latin cava, from cavum, cavus), ultimately from Proto-Indo-European *ḱówHwos (“cavity”). Compare Portuguese cova. Not related to English cove, despite the similarity in meaning.
köken: Borrowed directly from Italian grotta or indirectly via French grotte, from Latin crypta, from Ancient Greek κρυπτός (kruptós). Doublet of crypte, krocht, and gruft.
From Middle Welsh gocof, cf. Old Welsh guocobauc ‘cavernous’ (modern ogofog), from Proto-Celtic *uɸo-kubā, according to Pokorny, from Proto-Indo-European *kew- (“bend”). Cognate with Cornish gogow and Breton gougoñv.