vigilantly

From vigilant +‎ -ly.

vigilantly (comparative more vigilantly, superlative most vigilantly)

1. In a vigilant manner.
   • 1899 February, Joseph Conrad, “The Heart of Darkness”, in Blackwood’s Edinburgh Magazine, volume CLXV, number M, New York, N.Y.: The Leonard Scott Publishing Company, […], →OCLC, part I, page 204:

     He shuffled athwart, keeping one eye ahead vigilantly.