Rebus
2 of the 7 encyclopedias on this shelf carry an entry for Rebus. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a word, name, sentiment or pithy saying set forth in pictures or various devices, such as the position of words, syllables, letters, etc., with reference to some other part of the rebus. Like the charade, the rebus serves for parlor amusement. A few may be given by way of illustration: :A An American author and one of his chief works. The answer is: Mark Twain , Innocents Abroad (in no sense, A broad). In the same way Wyandotte, a town in Kansas, is represented by Y. The following, based entirely on the position of syllables, purports to be a post-office address: hill John Mass. The postal authorities are supposed to interpret: John Underhill, Andover, Massachusetts. A variety of rebuses may be expressed in a simple way by a picture or two, as: A noted discoverer--A column and an omnibus. A state of the American union--Noah's ark and a handsaw. A city of Massachusetts--A sail bearing the letter M. The Keystone state--A lead pencil, a weather vane and A.
Collier's New Encyclopedia (1921)
a word, name, or phrase represented by the figure of an object which resembles in sound the words, or syllables of the words, indicated; an enigmatical representation of words by the use of figures or pictures; thus, a "bolt" and a "tun" represent "Bolton." In heraldry, a device intended to represent a proper name by a picture; a bearing or bearings on a coat of arms, containing an allusion to the name of the owner; as in the coat of the family of Arches, which consists of three arches.