Where does “sea slug” come from?

sea slug (English) comes from English sea, from Middle English see, from Old English sǣ, from Proto-West Germanic saiwi, from Proto-Germanic saiwiz, from Proto-Germanic sīhwaną, from Proto-Indo-European seykʷ-, from Proto-Indo-European sey- — to be wet; dribble; run; to stretch one's arm;...

sea slug (English): Any marine invertebrate with a visual resemblance to terrestrial slugs (land slugs)

Definitions

  1. Any marine invertebrate with a visual resemblance to terrestrial slugs (land slugs)

Ancestry of “sea slug”, step by step

sea slug traces back through two separate lines of ancestry.

via English sea

StepLanguageWordMeaning
1EnglishseaA large body of salt water; A lake, especially if...
2Middle Englishseesea, ocean; A body of water, a lake; seat, chair
3Old Englishsea, lake
4Proto-West Germanicsaiwisea
5Proto-Germanicsaiwizsea, ocean
6Proto-Germanicsīhwanąto filter
7Proto-Indo-Europeanseykʷ-to moisten; to filter
8Proto-Indo-Europeansey-to be wet; dribble; run; to stretch one's arm;...

via English slug

StepLanguageWordMeaning
1EnglishslugAny of many terrestrial pulmonate gastropod...
2Middle Englishsluggelazy person
3Old English*sliċ
4Proto-Germanic*sliki
5Proto-Germanic*slikiz
6Proto-Indo-Europeansleyǵ-to glide, smooth, spread; to smear; to creep; to...
Every word from Proto-Indo-European sey-