The Greek arithmos means a number — a specific count, amount, or quantity. It is the standard Greek word for number, from which English derives 'arithmetic.'
Arithmos appears throughout the New Testament in both literal (Luke 22:3; Acts 4:4; 6:7) and symbolic (Revelation) uses. Acts 4:4 records that the number (arithmos) of men who believed grew to about five thousand after Peter's sermon. The most theologically loaded use is in Revelation 13:18 — 'Let the person who has insight calculate the number of the beast, for it is the number of a man. That number is 666.' In Revelation, numbers carry symbolic weight (7 = completion, 12 = tribes/apostles, 144,000 = the complete covenant people). Arithmos reminds us that God is precise — He numbers His people, His stars, and His days.