Bum \Bum\, n. [Contr. fr. bottom in this sense.]

The buttock. [Low] --Shak.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Bum \Bum\, v. i. [imp. & p. p. Bummed; p. pr. & vb.n. Bumming (?).]

[See Boom, v. i., to roar.]

To make murmuring or humming sound. --Jamieson.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Bum \Bum\, n. A humming noise. --Halliwell.

Source: Webster's Revised Unabridged Dictionary (1913)