English
seaduck
From sea + duck.
Proto-Germanic *saiwiz ‘sea, lake’
Proto-West Germanic *saiwi ‘body of water’
Old English sǣ
Middle English see ‘sea’
English sea
Proto-Germanic *dūkaną ‘to dip, dive, bend down, stoop, duck’
Proto-West Germanic *dūkan ‘to dive, dive under’
Old English *dūcan ‘to dip, dive, duck’
Middle English ducken ‘to duck, plunge under water, submerge’
English duck
Today it means
noun Any large duck found in coastal waters, especially those of the subfamily Merginae.
Language periods are conventional ranges, not dates for this word.
Etymograph / seaduck