Warning, a.
Giving previous notice; cautioning; admonishing; as, a warning voice. That warning timepiece never ceased. Longfellow. Warning piece, Warning wheel (Horol.), a piece or wheel which produces a sound shortly before the clock strikes.
1 other Webster entry under this spelling
Warning, n.
1. Previous notice. "At a month's warning." Dryden. A great journey to take upon so short a warning. L'Estrange.
2. Caution against danger, or against faults or evil practices which incur danger; admonition; monition. Could warning make the world more just or wise. Dryden.
Shades of meaning
Fernald has no entry of its own for warning; he lists it under example.
Where he writes about it:
From its original sense of sample or specimen (L. exemplum) example derives the seemingly contradictory meanings, on the one hand of a pattern or model, and on the other hand of a warning--a sample or specimen of what is to be followed, or of what is to be shunned. — from example