-or

CIDE DICTIONARY

-or, suff. [L. -or: cf. OF. -or, -ur, -our, F. -eur.].

•  A noun suffix denoting an act; a state or quality; as in error, fervor, pallor, candor, etc.  [1913 Webster]
•  A noun suffix denoting an agent or doer; as in auditor, one who hears; donor, one who gives; obligor, elevator. It is correlative to -ee. In general -or is appended to words of Latin, and -er to those of English, origin. See -er.  [1913 Webster]

OXFORD DICTIONARY

-or, suffix forming nouns denoting a person or thing performing the action of a verb, or an agent more generally (actor; escalator; tailor) (see also -ATOR, -ITOR).

-or, suffix forming nouns denoting state or condition (error; horror).

-or, suffix forming adjectives with comparative sense (major; senior).

-or, suffix US = -OUR(1).