nym·phet 
(nĭm-fĕt, nĭmfĭt)
(nĭm-fĕt, nĭmfĭt)n.
A pubescent girl regarded as sexually precocious.
[From earlier nymphet, nymphette, small nymph, young nymph (applied in Vladimir Nabokov's novel Lolita (1955) to a pubescent girl desired by the novel's narrator) : NYMPH + -ET.]