Innocuous
Etymology
From Latin "innocuus," "harmless," from "in-" ("not") and "nocēre" ("to harm, to hurt"). The same "nocēre" root sits inside noxious and, distantly, innocent. English took the word whole in the 17th century, keeping the plain meaning of doing no harm.
adjective · /ih-NOK-yoo-us/
Harmless; unlikely to offend, injure, or cause trouble.
What it names
Something that looks or is entirely safe — an innocuous question, an innocuous remark — often used just before revealing that it was not so harmless after all.
Example
What seemed an innocuous change to the settings quietly deleted everyone’s saved files.
Related idea
Near nominal only loosely; the truer contrast is with egregious — the egregious act does conspicuous harm, while the innocuous one does none at all.