a current of water below the surface and flowing in a direction contrary to the water on the surface
Word origin
[1500–10; under- + set]This word is first recorded in the period 1500–10. Other words that entered Englishat around the same time include: arsenal, canvass, internal, investigate, lowlandunder- is a prefixal use of under, as to indicate place or situation below or beneath (underbrush; undertow); lower in grade or dignity (undersheriff; understudy); of lesser degree, extent, or amount (undersized); or insufficiency (underfeed)