Where does “demonstrationist” come from?

demonstrationist (English) comes from English demonstration, from Old French demonstration, from Latin demonstratio, from Latin -tiō, from Latin dissertātiō, from Latin dissertus, from Latin disserere, from Latin dis- — small stone, pebble; gravel, rubble.

Ancestry of “demonstrationist”, step by step

demonstrationist traces back through two separate lines of ancestry.

via English demonstration

StepLanguageWordMeaning
1EnglishdemonstrationThe act of demonstrating; showing or explaining...
2Old Frenchdemonstration
3Latindemonstratioindication, description, designation,...
4Latin-tiōtion, -ation, -ing
5Latindissertātiō(spoken) dissertation, discourse, disquisition
6Latindissertusarranged, disposed; explained
7Latindissereresecond-person singular future passive indicative...
8Latindis-asunder, apart, in two; reversal, removal;...
9Latincalceusshoe
10Latincalxlimestone; chalk; the finish line
11Ancient Greekχάλιξsmall stone, pebble; gravel, rubble

via English ist

StepLanguageWordMeaning
1EnglishistA practitioner or supporter of an ism
2English-istAdded to words to form nouns denoting
3Old French-iste
4Latin-ista-ist; one who practises or believes
5Ancient Greek-ιστήςAlternative form of -τής; -ist
6Ancient Greek-τήςAppended to verbs to form agent nouns
7Proto-Hellenic-tās
Every word from Ancient Greek χάλιξEvery word from Latin -tiōEvery word from Latin dis-