A Syriac word (hanpe/hanfe) meaning renegade. The word "Hanif" occurs 12 times in the Qur'an, where Abraham is looked upon as a model of "Hannifaya". According to Âl 'Imran 3:67, he is neither Jew nor Christian. Arab poets of pre-Islamic days used the term "Hanif" for a pagan or idolator. Even Muslim scholars recognized that the word is foreign. Masaudi in "Tanbih" says it is Syriac. The Syriac Christians used it as an equivalent of the pagan, or for non-Trinitarian heretics, eg. Arians. During the early days of Islam, the followers of the prophet prefered not to call themselves "Hunafa", and chose to use Muslim instead.
Four Hanifs were mentioned by ibn Ishaq, a famous biographer of Muhammad: Waraqa b. Naufal, Ubaidullah b. Jash, Uthamn b. al-Huwayrith and Zaid b. Amr.
One day when the Quraysh had assembled on a feast day to venerate and circumambulate the idol to which they offered sacrifices, this being a feast which they held annually, four men drew apart secretly and agreed to keep their counsel in the bonds of friendship. They were Waraqa b.Naufal, Ubaydullah b.Jahsh, whose mother was Umayma d.'Abdu'l Muttalib, Uthman b.al-Huwayrith and Zayd b.'Amr. They were of the opinion that their people had corrupted the religion of their father Abraham, and that the stone they went round was of no account, it could neither hear nor see, nor hurt nor help. ``Find yourselves a religion,'' they said, ``for by God you have none.'' So they went their ways seeking the ``Hanaffiya'' -- the religion of Abraham." (Ibn Ishaq, Life of Muhammad, tr. Guillaume, p. 99)
It is interesting that these four monotheists did not believe in the pagan ritual of circumabulating the Ka'aba. The ritual was later adopted by the Muslims.
Richard Bell makes an interesting suggestion regarding the puzzling question of the identity of the hanifs in his article Who were the Hanifs?