: a game in which one shouts “beaver” when one sees a bearded person
The Oxford English Dictionary provides the following citation for this use of the word beaver:
This amazing game of Beaver … is played … by two persons, and the points are scored as in tennis. Whichever of the two first cries ‘Beaver!’ as a beard heaves into sight, scores.
— The New Statesman, 12 Aug. 1922
A resurgence of this game is, we think, long overdue.
The word beaver has since the mid-20th century also been used to mean "to work energetically"; omitted from that definition but theoretically plausible nonetheless is the notion that a bearded person identified in the game beaver might pretend at great busyness in order to escape the attention drawn to them.