Noun: a fancy, ridiculous word used in old-timey poetry. Now used as a creative and unique insert for swear words - mainly shit.
Old-Timey Example: "Ah! as the heart grows older
It will come to such sights colder
By and by, nor spare a sigh
Though worlds of wanwood leafmeal lie"
Modern Examples: "What a steaming pile of leafmeal!"
"This is such a crock of leafmeal."