1With a stare; with eyes wide open; in such a manner as to stare.
2Specifically. With reference to perturbation or mental disturbance: wildly, frantically. Now somewhat rare.
3So evidently or obviously as to ‘stare one in the face’; glaringly; palpably.
Late 16th century; earliest use found in Claudius Hollyband (fl. 1573–1583), linguist and writer. From staring + -ly.