Merriam-Webster Collegiate Dictionary - wahoo

 I. noun  (plural ~s)  Etymology: origin unknown  Date: 1770 winged elm  II. noun  (plural ~s)  Etymology: Dakota wahu, from wa- arrow + hu wood  Date: 1857 a shrubby spindle tree (Euonymus atropurpureus) of chiefly eastern North America that has purple capsules which in dehiscence expose scarlet-ariled seeds — called also burning bush  III. noun  (plural ~s)  Etymology: origin unknown  Date: circa 1900 a large vigorous mackerel (Acanthocybium solandri) that is common in warm seas and esteemed as a food and sport fish  IV. interjection  Date: circa 1924 chiefly West — used to express exuberance or enthusiasm or to attract attention