"un" translates as "one", it's not a part of the body.
a bottom (body part) is called 'un derrière' (masc.) in French
a lion is called 'un lion' in French.
a peacock is called "un paon" in French (do not pronounce the "o" in the word)
A bed is 'un lit' in French.
"un cheval" is a horse in French.
a jumper is called "un pull / un pullover / un sweat" in French
The rhino is called "un rhino / un rhinocéros" in French.
A knife in French is called "un couteau."
a raincoat is 'un imperméable' or 'un manteau' in French.
un lapin = rabbit
A tram (streetcar) is called 'un tram' or 'un tramway' in French.
Pomegranate is called "grenade" in French.