a self-seeking, servile flatterer; fawning parasite.
From the World Dictionary:
a person who uses flattery to win favour from individuals wielding influence; toady.
1537 (in L. form sycophanta ), “informer, talebearer, slanderer,” from L. sycophanta, from Gk. sykophantes, originally “one who shows the fig,” from sykon “fig” + phanein “to show.” “Showing the fig” was a vulgar gesture made by sticking the thumb between two fingers, a display which vaguely resembles a fig, itself symbolic of a c**t (sykon also meant “vulva”). The story goes that prominent politicians in ancient Greece held aloof from such inflammatory gestures, but privately urged their followers to taunt their opponents. The sense of “mean, servile flatterer” is first recorded in Eng. 1575.
**Yes, the “c” word. I thought the story entertaining, but removed the word that so many find offensive.