köken: From Middle High German regenwurm, from Old High German reganwurm, from Proto-West Germanic *regnawurmi. Analysable as Regen (“rain”) + Wurm (“worm”), so called because of the animal’s habit of surfacing after rainfall. Cognate with Old English reġnwyrm, whence English rainworm.
köken: First cited to the Saibara Uta from the Heian period. The memezu form is attested from 1650, and is traditionally viewed as a pronunciation shift from mimizu. Reconstructed as ultimately from Proto-Japonic *memensu, in which case memezu may be a reversion to an older form, also preserved in many dialects. The kanji are jukujikun (熟(じゅく)字(じ)訓(くん)).
köken: Nativisation of the Sino-Korean term 지룡 (地龍, jiryong, “earthworm”) + -이 (-i, noun suffix). First attested as Middle Korean 디로ᇰ이 (Yale: tilwong.i) in the Bunmun onyeok ihaebang (分門瘟疫易解方 / 분문온역이해방), 1542.
köken: dagg (“dew”) + mask (“worm”), used since 1753 in the current sense (Lumbricus terrestris), but earlier of other worms and snails (without a shell), compare English dewsnail.
köken: Inherited from Proto-Slavic *dъždževьnica. By surface analysis, Old Polish deżdż + -ownica, (genitive dżdżu). Compare near cognate Bulgarian дъждовник (dǎždovnik), Slovak dážďovka. The name refers to the fact that these worms can usually be spotted at the surface after heavy rain; compare English rainworm, German Regenwurm. Doublet of deszczownica.