The area offshore beyond the 100 fathom line, too deep to be fathomed by a hand sounding line, was referred to as "offsoundings" or "out of soundings".
Even when you have discovered all properties of monsters, wands, potions, and have fathomed the role of luck, the game remains as playable as ever.
Rachmaninoff himself may simply have not fathomed the true nature of this composition, especially when it was first performed.
Famously his final words are reputed to be can not be fathomed.
That trust cannot be fathomed or weighed.
At the moment they are indicating that they have not yet fathomed what it is that is being proposed.
