A very sturdy, heavy tool. A cross between the words "man" (humanity as a whole) and "anvil" (a hard and massive block of stone or metal used as a support for chiseling and hammering).
You'd need a crane and a bulldozer to get that ugly manvil up the stairs.
A particularly large and massive penis.
A fusion of "Man" and "Anvil".
"I dropped the manvil on that poor cuntlip last night."