You'll ride on a horſe that was foal'd of an acron.
That is; the gallows.

"What ho, my kiddy!" cried Job, "don't be glimflashy; why you'd cry beef on a blater; the cove is a bob cull, and a pal of my own; and moreover, is as pretty a Tyburn blossom as ever was brought up to ride a horse foaled by an acorn."

Fourteen, sir. No age to be riding a horse foaled by an acorn, I can tell you.

A sheep stealer, the mother told the child... and now the man twisted there, riding a horse foaled by an acorn, as the saying went, while the fat Welsh sheep in safety grazed the green pasture all around.

Ride a horse foaled by an acorn

Meaning

Verb