The adjective anarithmētos means innumerable or beyond counting — too vast to be enumerated. It appears once in the New Testament (Hebrews 11:12), describing the innumerable descendants promised to Abraham, as numerous as the stars of the sky and the sand of the seashore.
The promise of innumerable descendants was made to Abraham when he had no children and his wife was barren (Genesis 15:5, 22:17). Against all human probability, God spoke of anarithmētos offspring. Hebrews 11 holds up Abraham as the supreme example of faith — believing the innumerable promise while holding a single, miracle-born son. This tension between the singular and the countless is the heartbeat of biblical faith: trusting God's word about an unseen multitude while holding only what is visible in hand. The fulfillment is both physical (the nation of Israel) and spiritual (the church as Abraham's family of faith from every nation — Galatians 3:29).