Origin: Latin suffix -ory
Explanatory has 2 different meanings across 1 category:
serving or intended to explain or make clear
"explanatory notes"
"an explanatory paragraph"
Intended to serve as an explanation.
"The teacher provided an explanatory note on the board to clarify why the experiment failed."
In plain English: Something that is explanatory gives you clear reasons for why something happened.
"The teacher provided an explanatory note to clarify why the test was canceled."
The word explanatory comes from the Late Latin explānātōrius, which is derived from the verb meaning "to explain." It eventually entered English to replace the older term gereclīc.