-ator

suff.

One that acts in a specified manner: radiator.

[Latin -ātor : -ā-, stem vowel of verbs in -āre + -tor, agent n. suff. (later reanalyzed as -ātus, -ate + -or, -or).]

American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

-ator

suffix forming nouns

a person or thing that performs a certain action: agitator; escalator; radiator.

[from Latin -ātor; see -ate¹ -or¹]

Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

-ator

a suffix that forms nouns corresponding to verbs ending in -ate¹, denoting a human agent (agitator; mediator) or nonhuman entity, esp. a machine (incubator; vibrator) performing the function named by the verb. Compare -tor, -or².