from Wiktionary, Creative Commons Attribution/Share-Alike License
- adv. In an intent manner, intently; with close attention, attentively
from the GNU version of the Collaborative International Dictionary of English
- adv. Attentively; observingly.
from The Century Dictionary and Cyclopedia
- Silently; with mute attention; earnestly.
Possibly an alternative form of whistly, or whishtly ("quietly"). (Wiktionary)