I don't understand the difference between those words.
The Collins dictionary defines executor as "one who executes," and then defines executer as:
executer (noun)
= executor
I use executor for entity which execute commands (for example, names like "SendEmailExecutor" or "ChangePasswordExecutor").
Is there a time when I should use executer instead? Or are they always interchangeable?
"Executor" has a specific meaning. It's a legal term referring to the person who manages a deceased person's estate in accordance with that person's will. It's pronounced differently too, the emphasis is on the second syllable. Here is a definition with pronunciation.
"Executer" is pronounced with the emphasis on the first syllable. It means the one who executes. That may mean (arguably incorrectly) to execute a will as in the above. Among other meanings it may also mean the one who carries out the execution of a person, as in hangman. Many dictionaries don't even list it as a word (executioner is much preferred in the hang-man context), but here is one that pronounces it.
"Executor" is absolutely the preferred way to spell the legal term. Some (myself included) would say that the "er" would be incorrect in that context. If I were using it to mean hangman, I would use the "er" and pronounce it that way. But even in that context, some would argue that it's a made-up word.
For your purpose, I would endeavor to avoid it entirely by coming up with a different word.
Executer with the "er" suffix is the actual man doing the action. as in giver or skier or promiser. Executor with the "or" is the indication of the agent "acting" for the party of interest. as in donor or promisor or trustor. Both words are in Webster's 1828 online dictionary and the definitions clarify this distinction. This role of the suffix to change the word (root) meaning seems to be pointed out where the legal fictions meet the real men in action. Like another is doer and it's legal fiction counterpart donor not seemingly related but the are. A don is a father or the main man the "doer" so to act for or with his power for him is a donor. Think donated power as in a power of attorney in this case a power of the father.
Many words in English (for whatever reason) have multiple spellings. It may be due to the way English came about: being a disorganised heap of other languages all merged into one, the chances are the two words, sharing the same meaning, had two different spellings according to these two language where they originated from.
I don't know if this is the case with 'executor', but it is certainly a word with two spellings, yet one meaning. Because 'executor' is the word defined, and 'executer' is simply the word that is equated to it, I would agree that 'executor' is more common to use. There is no context in which one is used more than the other. It may be used more in one dialect of English than another, according to accent for example, but in writing there is no difference. Nada.
Executioner is the word people mean when they think of "hangman, the one who executes someone"... Executer does not exist.
Executor has been dealth with here.
