(poetic) All of the oceans of the world. (In a common modern interpretation, the seven seas are the North and South Atlantic, North and South Pacific, Indian, Arctic and Antarctic, but historical interpretations differ widely; see the Wikipedia article for this.)

(Catholicism) The sacred counterparts of the seven deadly sins.

In Germany, June 27 is Siebenschläfertag (Seven Sleepers Day). The weather on that day is supposed to determine the average weather of the next seven weeks.

singular of seven-league boots

(historical) A war fought between 1754 and 1763 between almost every European great power of the time, partly over colonies and partly over Austria's desire to recover Silesia from the Prussians. The main conflict occurred in the seven-year period from 1756 to 1763.

(colloquial) Scabies. / (colloquial) The temptation to have an affair after seven years of being married.

Seven Wonders of the Ancient World / New Seven Wonders of the World

A plastic-handled (officially yellow) pocket screwdriver (with clip) and a 2.5 inch shank, ending in a 1/8 inch slotted head.

A cake consisting of seven thin layers of baked batter interlaced with seven layers of frosting.

Synonym of at sixes and sevens