Laughing falcon (Zoö]l.), a South American hawk (Herpetotheres cachinnans); -- so called from its notes, which resemble a shrill laugh. -- Laughing gas (Chem.), hyponitrous oxide, or protoxide of nitrogen; -- so called from the exhilaration and laughing which it sometimes produces when inhaled. It is much used as an anæsthetic agent. -- Laughing goose (Zoöl.), the European white-fronted goose. -- Laughing gull. (Zoöl.) (a) A common European gull (Xema ridibundus); -- called also pewit, black cap, red-legged gull, and sea crow. (b) An American gull (Larus atricilla). In summer the head is nearly black, the back slate color, and the five outer primaries black. -- Laughing hyena (Zoöl.), the spotted hyena. See Hyena. -- Laughing jackass (Zoöl.), the great brown kingfisher (Dacelo gigas), of Australia; -- called also giant kingfisher, and gogobera. -- Laughing owl (Zoöl.), a peculiar owl (Sceloglaux albifacies) of New Zealand, said to be on the verge of extinction. The name alludes to its notes.