[1905–10 in sense “underwear”; 1935–40 for current sense; under- + wool]This word is first recorded in the period 1905–10. Other words that entered Englishat around the same time include: Expressionism, one-shot, stabilizer, thiamine, white listunder- 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)