settler vs treater

settler and treater both are nouns.

Word	Noun	Adjective	Verb	Adverb
settler	Yes	No	No	No
treater	Yes	No	No	No

As nouns, treater is a hypernym of settler; that is, treater is a word with a broader meaning than settler:

settler: a negotiator who settles disputes
treater: someone who negotiates (confers with others in order to reach a settlement)

Other hypernyms of settler include negotiant, negotiator.

settler (noun)	treater (noun)
a person who settles in a new colony or moves into new country	someone who negotiates (confers with others in order to reach a settlement)
a clerk in a betting shop who calculates the winnings
a negotiator who settles disputes