The Greek noun kalamos refers to a reed — the tall grass plant that grows in water, used for multiple purposes in the ancient world. It served as a writing pen, a measuring rod, a musical instrument, and in the Passion narrative, as a mock scepter and a sponge-bearer for Jesus.
Kalamos appears in the Passion account where soldiers put a reed in Jesus' hands as a mock scepter (Matthew 27:29), then took it and struck him on the head (Matthew 27:30). The same word is used in 3 John 1:13 for a writing pen. In Revelation 11:1, John is given a measuring rod like a staff (kalamos) to measure the temple.
Theologically, the kalamos in the Passion narrative captures the cruel irony of the crucifixion: the King of kings was mocked with a reed scepter. But His true royal authority was being exercised in the very moment of apparent humiliation.