Meaning of Numbers: The Number 81
The possible meaning of the number 81 is derived from both the Bible and secular history.
Roman Emperor Titus began his rule in 79 with the death of his father Emperor Vespasian. Titus, as General in 70 A.D., led the Roman army to capture and destroy both Jerusalem and its Temple. This complete destruction was predicted twice by Jesus (Matthew 24:1 - 2, Luke 19:41 - 44). He dies in 81 A.D. with his younger brother Domitian replacing him as Emperor.
It was also in 81 A.D. that the new emperor instituted Rome's second official state persecution of Christians. This policy led, near the end of Domitian's reign, to the Apostle John being banished to the island of Patmos in 95. John would not be set free until the following year.
Rome's famous Arch of Titus, which graphically depicted the spoiling of Jerusalem and her temple, was begun in 81 after the death of the Emperor. The menorah pictured in the middle of the relief was used as the inspiration for modern Israel's emblem of state (Israel National Symbols).

Appearances of the Number Eighty-One
According to the Complete Book of Bible Lists, Scripture mentions at least 81 distinct animals. These include bats, cranes, crocodiles, dragons, eagles, fleas, leopards, owls, peacocks, pelicans, ravens, spiders, unicorns, weasels, whales, wolfs and worms! Surprisingly, no cats are mentioned in God's word.
The English word "servant" is found 85 times in 81 King James New Testament verses. It is recorded the most in Luke (25) followed by Matthew (22). It is usually derived from the Greek pais (Strong's Concordance #G3816) or doulos (Strong's #G1401).
The centurion answered and said, Lord, I am not worthy that thou shouldest come under my roof: but speak the word only, and my servant (pais) shall be healed (Matthew 8:8, KJV).
The disciple is not above his master, nor the servant (doulos) above his lord (Matthew 10:24, KJV).
The Greek word apostolos (Strong's #G652) is written 81 times in the original Greek of the New Testament. It is found the most in Acts (30 times) followed by 1Corinthians (10). The word means "he that is sent" and can be utilized to refer to a delegate, ambassador or messenger. Although it is translated, in the King James, as "apostle" it can refer to those who are not the original twelve picked by Christ.
Which when the apostles (apostolos), Barnabas and Paul, heard of, they rent their clothes, and ran in among the people, crying out . . . (Acts 14:14, KJV).
Paul, a servant of Jesus Christ, called to be an apostle (apostolos), separated unto the gospel of God (Romans 1:1, KJV).
Number 81 and the Psalms
Psalm 81 is one of twelve songs written by or for Asaph. He served as one of Kind David's chief musicians who played instruments and sung at the temple (1Chronicles 15:17, 19).
The book of Psalms, in the original Hebrew manuscripts of the Old Testament, is divided into five sections. Psalm 81 is in the third section that contains chapters 73 to 89. The general theme of the third section is the destruction of Jerusalem and the Temple.
This song is one of rejoicing for God's deliverance out of the bondage of Egypt.
Sing aloud unto God our strength; shout for joy to the God of Jacob. Take up a melody, and strike the drum, the pleasant lyre with the harp.
Blow the trumpet at the new moon, also at the full moon, on our solemn feast day . . . I am the Lord your God Who brought you out of the land of Egypt; open your mouth wide, and I will fill it . . . (verses 1 - 3, 10, HBFV).
More Info on Biblical Meaning of 81
81 is the product of 3 x 3 x 3 x 3 (3 to the fourth power). 3 is a prime number.
God commanded ancient Israel, ever seven years, to observe what is known as a Sabbatical year (Leviticus 25:1 - 7, 19 - 23). One of these special years began on September 2 in 81 B.C. and ended on September 21 in 80.
In a unique coincidence, September 22 in 81 A.D. also began a Sabbatical year. This period ended September 12 in 82 A.D.
The only Biblical book to contain 81 verses is 1Chronicles 6.
Moses was eighty years old when he confronted Pharaoh in Egypt (Exodus 7:7). He was 81 when the Israelites kept their second Passover in the wilderness of Sinai (Numbers 9:1). He was also this age when, due to a lack of faith, the Israelites were punished with wandering the wilderness for forty total years (chapters 13, 14).