Sydyk (, in some manuscripts Sydek or Sedek) was the name of a deity appearing in a theogeny provided by Roman-era Phoenician writer Philo of Byblos in an account preserved by Eusebius in his Praeparatio evangelica and attributed to the still earlier Sanchuniathon.
Philo of Byblos gave the Greek meaning of the name as ? "Righteousness", thus indicating that the word corresponds to the Semitic root for "righteousness", dq. A Phoenician god named ?dq is well attested epigraphically; he is also mentioned by Philo as half of a pair of deities with Misor (). Sydyk and Misor are described as being born from Amunos and Magos, who were in turn born from the "Wanderers" or Titans. Sydyk is described as the father of the "Dioskouroi or Kabeiroi or Korybants or Samothracians", who are credited with the invention of the ship.
A connection between Sydyk and the Assyro-Babylonian deity Kittu has been proposed. The latter was also referred to as ?idqu and additionally the West Semitic name Ammi-?aduqa is translated into Akkadian as Kimtum-kittum showing an equivalence of meaning between the West Semitic ?-d-q and the Akkadian kittu. Kittu was similarly paired with the god Misharu, whose name is a cognate of Misor "justice". In Mari the equivalent deities of I?ar and Me?ar are found.
It has also been conjectured that a related deity named or titled "Tzedek" (i.e. "righteousness") was worshipped in pre-Israelite Jerusalem as the names of two kings of the city, Melchizedek and Adonizedek contain the element tzedek. According to one such hypothesis "Tzedek" was an epithet of the god El (). However the mainstream understanding of these names (meaning "My King is Righteousness" and "My Lord is Righteousness" respectively) is that they refer to the concept of righteousness and not to a god.