In the end of Book VI of the Odyssey, Odysseus sends up a pray to Athena, the Greek goddess of Wisdom and Warfare. It then says Athena does not openly acknowledge him. The reason being that she feared Poseidon's wrath.
 So saying, she smote the mules with the shining whip, and they quickly left the streams of the river. Well did they trot, well did they ply their ambling feet, and she drove with care that the maidens and Odysseus might follow on foot, and with judgment did she ply the lash. Then the sun set, and they came to the glorious grove, sacred to Athena. There Odysseus sat him down, and straightway prayed to the daughter of great Zeus: “Hear me, child of aegis-bearing Zeus, unwearied one. Hearken now to my prayer, since aforetime thou didst not hearken when I was smitten, what time the glorious Earth-shaker smote me. Grant that I may come to the Phaeacians as one to be welcomed and to be pitied.”
 So he spoke in prayer, and Pallas Athena heard him; but she did not yet appear to him face to face, for she feared her father's brother; but he furiously raged against godlike Odysseus, until at length he reached his own land.
Retrieved from here, on: 3/23/2018
Why would Athena fear Poseidon? Isn't Athena stronger than Poseidon?