🔼The name Didymus in the Bible
There's only one Didymus in the Bible, and he was one of the Twelve Apostles of Jesus Christ. Only John mentions the name Didymus (John 11:16, 20:24, 21:2), which is the Greek translation of his more common Semitic name Thomas, which occurs in all four gospels and Acts.
🔼Etymology of the name Didymus
The name Didymus is a common Greek word that means double or twofold. Liddell and Scott (A Greek-English Lexicon) state that our word is formed from a reduplication of the familiar word δυο (duo), meaning two:
Our word διδυμος (didumus) may denote working with both hands or being forked. It was the common word for twin, and in plural (διδυμοι, didumoi, meaning twins) it was applied to the Twins of the zodiac, also known as Dioscuri. The same plural word could describe a man's testicles or a woman's ovaries.
The name Didymus means Twin, but it should be noted that it wasn't commonly used as a name. The name Thomas, though later very popular, was also quite uncommon.