ETYMOLOGY
– probably from undercumstumble (to understand, Eng. dial.)
EXAMPLE
“…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…”
From: Greatheart
By Walter Thornbury, 1866
Lexicophilia 