Monoimus (lived somewhere between 150 - 210) was an Arab gnostic (Arabic name probably Mun'im منعم), who was known only from one account in Theodoret (Haereticarum Fabularum Compendium i. 18) until a lost work of anti-heretical writings (Refutation of All Heresies, book 8, chapter V) by Hippolytus was found. He is known for coining the usage of the word Monad in a gnostic context.

Hippolytus claims that Monoimus was a follower of Tatian, and that his cosmological system was derived from that of the Pythagoreans, which indeed seems probable. But it was also clearly inspired by Christianity, monism and Gnosticism.

According to Monoimus, the world is created from the Monad (or iota, or Yod meaning "one horn"), a tittle that brings forth the duad, triad, tetrad, pentad, hexad, heptad, ogdoad, ennead, up to ten, producing a decad. He thus possibly identifies the gnostic aeons with the first elements of the Pythagorean cosmology. He identifies these divisions of different entities with the description of creation in Genesis. This description from Hippolytus also corresponds to two versions of a text called Eugnostos found in Nag Hammadi, where

He is also famous for his quote about the nature of God, which may be described as pantheistic (from Hippolytus):

Omitting to seek after God, and creation, and things similar to these, seek for Him from (out of) thyself, and learn who it is that absolutely appropriates (unto Himself) all things in thee, and says, "My God my mind, my understanding, my soul, my body." And learn from whence are sorrow, and joy, and love, and hatred, and involuntary wakefulness, and involuntary drowsiness, and involuntary anger, and involuntary affection; and if you accurately investigate these (points), you will discover (God) Himself, unity and plurality, in thyself, according to that tittle, and that He finds the outlet (for Deity) to be from thyself.

This idea resembles the viewpoint of the much later Sufi Ibn Arabi, but no connection between the two is known.