Sizar,

Chambers's Encyclopaedia, Volume 9: Bound to Swansea, p. 481

Sizar, the name of an order of students at Cambridge and Dublin universities, so called from the allowance of victuals (size) made to them from the college buttery. Duties of a somewhat menial kind, such as waiting upon the fellows at table, were originally required of the sizers, but these have long since gone into disuse. At Oxford there was formerly a somewhat similar order of students denominated Servitors.

Source scan(s): p. 0494