Wiktionary
fathomlessly
adv. In a fathomless manner.
Usage examples of "fathomlessly".
Time paced slowly toward the eternity, and space was fathomlessly black.
It eyed him fathomlessly out of eyes of liquid purple, then reached up above his head to nibble at a pine bough.
Brown eyes met black, the former angrily determined, the latter fathomlessly dark.