Etymology

Middle English waggen, noun wagge, feminine root of Old English waian, (Middle English noun wae) to oscillate, shake. Compare the Old English verb waġian

The verb may be regarded as an iterative or emphatic form of waian waw, verb, which is often nearly synonymous; it was used, e.g., of a loose tooth. Parallel formations from the same root are the Old Norse vagga femimine, cradle (Swedish vagga, Dutch vugge), Swedish vagga to rock a cradle, early modern German waggen (modern High German dialect wacken) to waver, totter. Cf. waggle, verb

Verb

1. To swing from side to side, especially of an animal's tail
2. To not go to school, either for a class or classes or the entire school day;¹ play the wag; hop the wag; wag it.²
   • 1848, Charles Dickens, Dombey and Son, xxii

     "My misfortunes all began in wagging, Sir; but what could I do, exceptin' wag?" "Excepting what?" said Mr. Carker. "Wag, Sir. Wagging from school." "Do you mean pretending to go there, and not going?" said Mr. Carker. "Yes, Sir, that's wagging, Sir."

   • 1901, William Sylvester Walker, In the Blood, i. 13

     They had "wagged it" from school, as they termed it, which..meant truancy in all its forms.

Noun

1. An oscillating movement.

   The wag of my dog's tail expresses happiness.

2. A witty person.