to thoroughly understand, to detect, to suspect ...1866
a variant of undercumstumble, which is an alteration of undercumstand (vb. to understand)
FIRST DOCUMENTED USE
1866 - see EXAMPLE below
"...Well, he stole on behind a rock, like a coastguard man watching a boat, and got very near the noise. He couldn't umble-cum-stumble the words - they were Greek and Hebrew to him; but the sound was for all the world like Bill Polworth's voice, when he used to sing second counter at St. Tudy's..."
- George Walter Thornbury