Definition from Wiktionary, the free dictionary
concubine (plural concubines)
- A woman who lives with a man, but who is not a wife.
- A slave-girl for sexual service prominent in all ancient cultures.
- Signifies a relationship where the male is the dominant partner, socially and economically
- A woman attached to a man solely for reproduction, and who cares for the resulting children without any romantic relationship.
- (especially formerly in Arabic societies, as well as in ancient Eastern societies) a woman residing in a harem and kept, as by a sultan or emperor, for sexual purposes.
- A woman kept by a man who is high in hierarchial society in addition to his wives, e.g in the imperial harem or within a household.
Derived terms 
a woman who lives with a man, but who is not a wife
slave-girl — see slave-girl
mistress — see mistress
See also 
- Random House Unabridged Dictionary
- Plural form of concubina
- vocative singular of concubīnus