väninna

Etymology
.

Noun

 * 1) a female friend (usually of a female, and usually of adult friendship)
 * 2)  a mistress (of a man)

Usage notes
Having a väninna sounds feminine. A female friend of a male would usually just be called a "(kvinnlig) vän" ((female) friend). Though rare in contemporary Swedish and likely to be misunderstood, a of a man can also mean a mistress.