The Collaborative International Dictionary
Fastly
Fastly \Fast"ly\, adv. Firmly; surely.
Douglas Harper's Etymology Dictionary
fastly
"quickly," c.1200, former adverbial cousin to fast (adj.), from Old English fæstlic "firmly, fixedly, steadfastly, resolutely;" obsolete in 19c., simple fast taking its place.
Wiktionary
fastly
Etymology 1 adv. securely. Etymology 2
adv. quickly
Usage examples of "fastly".
He moved slowly to the left, attempting to coax the thing into the light from the open doorway, but it kept stead fastly to the darkness.