Idly means without purpose or effort. Idly wondering, stood idly by, idly turning the pages.
It describes doing something without attention rather than doing nothing: idly leafing through a book is still leafing. Stand idly by is the fixed phrase for failing to act when you should, and it is nearly always a reproach. Note idle as adjective and verb; and that idly is one of the -ly adverbs formed from an adjective already ending in -le.
1adverbidlyWithout purpose or effort.
“She flicked idly through a magazine while she waited for the dentist.”
idly is a manner of aimlessness.
Old English idellice is idle plus -ly. Idle meant empty or worthless before it meant lazy, which is why an idle threat is an empty one.
Old English
īdellīċe
Middle English
idely
English, today
idly
From Middle English idely, ydelly, idelliche, from Old English īdellīċe, equivalent to idle + ly.
Etymology from Wiktionary, CC BY-SA