What's the difference between the "-teer" and "-ter" suffix?

Question

• RackeTEER, but not rackeTER
• PuppeTEER, but not puppeTER
• PrivaTEER, but not privaTER

Related: in my industry, we see both "marketer" and "marketeer."

Why? Is it just stylistic? Is there a semantic difference?

Answer 1

Oxford Languages says that the suffix -eer forming a noun means 'a person concerned with or engaged in an activity'. (Privateer was coined because the people concerned were private individuals and not naval personnel.)

-er is just the ordinary suffix to a verb meaning 'a person who does that activity'. So you can say marketer because market can be a verb as well as a noun, but puppet and private aren't verbs, and racket can be but not in this sense.

Answer 2

Every English word has a different history; if it's borrowed, which is likely, then it was borrowed at a particular time, from a particular speech group or dialect, by particular people, in a particular place, for their own particular reasons. And all of those particulars were different for each word in the language. And we don't know them and never will, though we can guess in some cases.

In the case of the -te(e)r agentive, I would guess (without looking it up in the dictionary, which could already have been done) that -teer words are French borrowings from words in -tier, while the others aren't. They're all from the same PIE root, but via different routes is my guess. But that's just a guess. There are about a million words in English, and nobody knows more than a tenth of them, let alone all their etymologies. Language is not so well organized as that.