The amazing noun σημειον (semeion) means mark, sign or token. It's the extended version of the noun σημα (sema) — hence our English word "semantic", which originally denoted a relevance to signs in general but became applied in particular to the meaning or connotations of words. Our noun σημειον (semeion) refers to a meaningful sign or symbol, and often occurs in conjunction with the noun τερας (teras), meaning sign in the sense of an attention grabber; a wonder.

Our Greek word σημειον (semeion) stems from an ancient Proto-Indo-European root dheie-, meaning to see or look, from which also stems the familiar noun Chan (in English mostly spelled Zen), which is the name of a form of Buddhism. Chan or Zen Buddhism originated in China in the first quarter of the first millennium but was a continuation of Indian Buddhism which had started in the fifth century BC, roughly around the time when the Jews returned from their Babylonian exile. There was and remained a strong cultural economic interaction between India and Persia and later the Greeks and the Roman Empire. Classical writers have recorded several instances Indo-Roman interactions, and around the time of Jesus, Indian Buddhists both toured China and visited the imperial courts in Rome.

In the Greek classics our word σημειον (semeion) could describe anything from a marker on a border, grave or monument to a signaling flag in battle, a figurehead on shields, even a password or secret handshake and all that. In logic our word denoted a "sign" such as an example, demonstration or other such proof, and the Stoics and Epicureans used this word to describe the observable as opposed to the unobservable but deductible (the same division is made in Hebrews 11:1). The medical profession used our word to describe representative symptoms of a certain disease. Mathematics used our word as synonym for στιγμα (stigma), or point (in the mathematical sense).

The shorter version of our word, σημα (sema), in particular was also used in the sense of a "sign from heaven" or omen or sign of portent. In that sense our word was specifically associated with the star Sirius, and while the names Simon and Simeon formally come from the Hebrew verb שמע (shama'), meaning to hear or obey, any speaker of Greek would have surely caught the association with our noun σημα (sema) and its associate noun σημειον (simeion; see below). Sirius has been known as the Dog-star since antiquity. The Hebrew word for dog is כלב (keleb), hence the name Caleb, which belonged to the friend of Joshua. The name Joshua, of course, is the Hebrew version of the Greek name Jesus. That's all a bit beyond common coincidence.

Also note that the familiar ☧ mark consists of the letters Χ (chi) and Ρ (rho). The term ΧΡ is short for χρηστος (chrestos), meaning pleasant or profitable. By the time of Constantine, this mark was used by scholars, who wrote it in the margins of texts to mark a passage they found striking. All this may have influenced the transition between the Way of Jesus Christ (the non-religious search for global convention based on natural law) as it existed in the first century, and the imperial Christianity that emerged in the fourth.

The short version of our word, σημα (sema), isn't used independently in the New Testament but does show up in a small list of compounds (see below). The longer version σημειον (semeion) is used 77 times; see full concordance.

The latter comes with only one true derivation, namely the verb σημειοω (semeioo), meaning to mark, to endow with a mark, sign, token or flag; to give a signal or to interpret something as a sign. In the New Testament this word occurs only once, namely in 2 Thessalonians 3:14.

As mentioned above, the noun σημα (sema) is the shorter version of the noun σημειον (semeion), meaning mark or marker, flag, token or sign. This shorter version isn't used independently in the New Testament but from it come the following derivations: