treatise vs pamphlet

treatise and pamphlet both are nouns.

Word	Noun	Adjective	Verb	Adverb
treatise	Yes	No	No	No
pamphlet	Yes	No	No	No

As nouns, pamphlet is a hyponym of treatise; that is, pamphlet is a word with a more specific, narrower meaning than treatise:

treatise: a formal exposition
pamphlet: a brief treatise on a subject of interest; published in the form of a booklet

Other hyponyms of treatise include dissertation, thesis, tract, monograph.

treatise (noun)	pamphlet (noun)
a formal exposition	a brief treatise on a subject of interest; published in the form of a booklet
	a small book usually having a paper cover