To be 'all at sixes and sevens'...'seven deadly sins'...'seven year itch'...and probably lots more, as it's a very symbolic number, frequently used in proverbs etc.
A Scottish Mason has 7 tassels on each side of his apron. Arabians had 7 holy temples. There are 7 ancient planets. The Goths had 7 deities. There are 7 days of the week. 7 dwarfs. 7 deadly sins. 7 orders of architecture. 7 seas. 7 sisters. The 7th son of a 7th son will be gifted.
'Seven pieces of heaven' Fry's Chocolate Creme. 'seven seas of Rhye', Queen. '7-Up', 'seven swans a-swimming', 'seven year itch', 'seven wonders of the world' - and seven named notes in an octave [doh!] :-)
Seven Seas
seventh heaven
seven-year itch
Seventeen magazine
sevenfold
Seven Wonders of the World
Seven Sisters constellation
Seventh-Day Adventists
Seven Years War
seven deadly sins
seven-league boots
the seventies (1970's)
working 24/7