You may complain that seven is not so much a word as a number, and you will be right, but only partly. For those who tease out the origins of words, there is a very clear relation between the English word (and its German relation, sieben), the Italian sette, and the Latin number septem. We English have lost the t, our Mediterranean friends have lost the p. And this relation may go further, to the Hebrew word for seven, shava', and its word for the seventh day, which we know in English as the sabbath (and from which, incidentally, the name Samstag descends.)
The name for the number is probably as old as the division of time into weeks of seven days - you might almost say as old as time itself, or as the moon, whose phases marked the weeks. The Hebrews regarded the seventh day as holy - a time to rest. But Christians gathered together on the first day, the day of Jesus' resurrection, and over time this day too came to be regarded as holy. By the fourteenth century, Sunday was known as "the new sabbath". But it is good to remember that Saturday, the seventh day, for all who read the account at the beginning of Genesis, was a day of completion. Sunday, the first day after the sabbath, was a day for new beginnings - a new creation.
Because seven signified completion, the Old Testament mentions numerous sets of seven. Noah took seven pairs of the clean animals into the ark, Abraham presented Abimelech with seven ewe lambs, Jacob served Laban seven years (and then another seven!) to gain Rachel as his wife, Pharaoh dreamed of seven fat and seven lean cows. Aaron sets up a candle-stand with seven candles (Numbers 8), there are seven pillars of wisdom (Proverbs 9), Daniel foresees that Nebuchadnezzar's insanity will last for seven "times".
Around Jesus' lifetime, there was a keen interest in numbers and their meaning. The Revelation to John shows that this interest spilt over into the Christian church, and here we see series of angels, of plagues, of seals - grouped in sevens: often with the seventh in a series of visions leading into a fresh group of seven. Indeed, there are visions of events lasting 1260 days, or 42 months, which is half of seven years: visions of things which are half way to completion.
It is this sense of completeness that led Peter to ask Jesus: "How often should I forgive? Seven times?" And Jesus' reply, "Seventy times seven," implies that our forgiveness should not only be complete, but abundant and overflowing - beyond caution, beyond all reasonable limits.
Sometimes, the meaning behind the number is not clear. We all know the story of the Feeding of the Five Thousand, with its five loaves and its twelve baskets. The five loaves possibly recall the five books of the Law, and the twelve baskets the twelve tribes of Israel. But Matthew also mentions the Feeding of the Four Thousand, with seven loaves and seven baskets: perhaps this recalls the seventy Gentile nations the Jews thought there were, just as the seven deacons appointed in Acts 6 served the "foreign" rather than the Hebrew widows (and the four thousand may recall the four winds of heaven, reaching to all the corners of the earth).
Since New Testament times, lists of seven have multiplied. Can you name the seven deadly sins? The seven gifts of the spirit? The seven virtues (three of them spiritual, and four of them cardinal)? Some of these lists go back to the Bible itself: the seven churches of Asia mentioned in Revelation, the seven "I am" sayings of Jesus and the seven "signs", or miracles, in John's Gospel. The seven words from the cross? God's sevenfold gifts are complete, and what is complete for God is abundant to overflowing for us!
HD
(And if you can't name those sins, see below!)
Deadly sins
Anger, envy, gluttony, sloth, pride, avarice, lust
Gifts of the spirit
Wisdom, understanding, counsel, fortitude, knowledge, piety, fear of the Lord (Is.11:2)
Virtues
Faith, hope, charity are the three theological virtues.
Justice, prudence, temperance and fortitude are the four cardinal virtues.
Churches of Asia
Ephesus, Smyrna, Pergamum, Thyatira, Sardis, Philadelphia, Laodicea.
I am the bread of life (John 6:5)
I am the light of the world(John 8:12)
I am the gate of the sheepfold (John 10:7)
I am the good shepherd (John 10:11)
I am the resurrection and the life (John 11:25)
I am the way and the truth and the life (John 14:6)
I am the true vine (John 15:1)
Signs
Turning Water into Wine
Healing the Nobleman's Son
Healing the Palsied Man
Feeding the Five Thousand
Walking on the Sea
Healing the Blind Man
Raising Lazarus
Words from the Cross
Father, forgive them, for they know not what they do (Luke 23:34)
Verily I say unto thee, Today shalt thou be with me in paradise (Luke 23:43)
Woman, behold thy son! ... Behold thy mother! (John 19:26-27)
Eli, Eli, lama, sabachthani? - My God, my God, why hast thou forsaken me? (Matthew 27:46)
I thirst (John 19:28)
It is finished (John 19:30)
Father into thy hands - I commend my spirit (Luke 23:46)