bum
UK[bʌm]US[bʌm]
n
A person who avoids work and lives off others; a lazy or worthless person
n
A vagrant or homeless person
n
Informal term for the buttocks
v
To get something by asking or begging; to scrounge
Etymology
The word 'bum' has a complex and somewhat obscure etymology, likely entering English from multiple Germanic sources. Its primary sense of a 'loafer' or 'idler' appears to derive from a German regional term 'Bummler', meaning a 'loafer' or 'stroller'. The anatomical sense referring to the buttocks is probably onomatopoeic in origin, imitating the sound of a blow or a soft impact, and may be related to the obsolete word 'bum' meaning the sound of a bittern. These two streams of meaning converged in English during the 19th century, with the 'vagrant' sense solidifying first, followed by the slang term for the posterior. The verb form, meaning to beg or scrounge, developed naturally from the noun describing a person who does exactly that.
Analysis
This word is a simplex loanword and tight Germanic root. Its core form has remained largely unchanged in English spelling and sound.
Examples
He was labeled a bum for refusing to get a job and constantly borrowing money.
The toddler fell down and landed right on his bum.
Can I bum a cigarette from you?