Where does “illust” come from?

illust (English) comes from Japanese イラスト, from Japanese イラストレーション, from English illustration, from Middle French illustration, from Latin illūstrātiō, from Latin -tiō, from Latin dissertātiō, from Latin dissertus — small stone, pebble; gravel, rubble.

Ancestry of “illust”, step by step

Step	Language	Word	Meaning
1	Japanese	イラスト	illustration
2	Japanese	イラストレーション	illustration
3	English	illustration	The act of illustrating; the act of making clear...
4	Middle French	illustration	—
5	Latin	illūstrātiō	the action of lighting up, brightening
6	Latin	-tiō	tion, -ation, -ing
7	Latin	dissertātiō	(spoken) dissertation, discourse, disquisition
8	Latin	dissertus	arranged, disposed; explained
9	Latin	disserere	second-person singular future passive indicative...
10	Latin	dis-	asunder, apart, in two; reversal, removal;...
11	Latin	calceus	shoe
12	Latin	calx	limestone; chalk; the finish line
13	Ancient Greek	χάλιξ	small stone, pebble; gravel, rubble

Every word from Ancient Greek χάλιξ →Every word from Latin -tiō →Every word from Latin dis- →