1670s, "device for measuring sizes, contrivance for sorting articles of various sizes," agent noun from size (v.). By 1863 as "person who measures or applies sizes."
Entries linking to sizer
size v.
c. 1400, "regulate, arrange, dispose" (a sense now obsolete), from size (n.) or shortened from a verb form of assize (n.). The meaning "make of a certain size" is from c. 1600; that of "classify according to size" is attested from 1630s. The verbal phrase size up "estimate, assess, take the measure of" is from 1847 and retains the "assessment" sense of size (n.). Related: Sized; sizing.