or Chrism signifies properly “the white cloth set by the minister at baptism on the head of the newly anointed with chrism”— i.e. a composition of oil and balm. In the Form of Private Baptism is this direction: “Then the minister shall put the white vesture, commonly called the chrisome, upon the child.” The child thus baptised is called a chrisom or chrisom child. If it dies within the month, it is shrouded in the vesture; and hence, in the bills of mortality, even to the year 1726, infants that died within the month were termed chrisoms. (The cloth is so called because it was anointed. Greek, chrisma, verb chrio, to anoint.)
“A' made a finer end and went away an it had been any chrisom child.” —Shakespeare: Henry
V., ii. 3.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894