I have the following from www.focloir.ie.

My question for the native speakers, or one who knows, is -- what is the difference in meaning or implied meaning between these two words?

What I'm really after is figurative, as in, one who separates wheat from chaff not in the sense of an agricultural worker but euphemistically, as in, separates out what is meaningful and valuable from a lot of surrounding nonsense. Can you help?

thresher

2 noun AGR, EMPL worker
buailteoir masc3
súisteoir masc

FGB distinguishes between them by saying that súisteoir is a person who threshes with a flail (súiste being the flail itself), whereas a buailteoir is a piece of equipment used for striking, beating, or threshing, rather than a person.

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I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.