seven (n.) Look up seven at Dictionary.com
Old English seofon, from Proto-Germanic *sebun (cf. Old Saxon sibun, Old Norse sjau, Old Frisian sowen, siugun, Dutch zeven, Old High German sibun, German sieben), from PIE *septm (cf. Sanskrit sapta, Avestan hapta, Hittite shipta, Greek hepta, Latin septem, Old Church Slavonic sedmi, Lithuanian septyni, Old Irish secht, Welsh saith).

Long regarded as a number of perfection (e.g. Seven wonders, seven sleepers, the latter translating Latin septem dormientes, seven against Thebes etc.), but in German a nasty, troublesome woman could be eine böse Sieben "an evil seven" (1662). Magical power or healing skill associated since 16c. with the seventh son ["The seuenth Male Chyld by iust order (neuer a Gyrle or Wench being borne betweene)," Thomas Lupton, "A Thousand Notable Things," 1579]. The typical number for "very great, strong," e.g. seven-league boots in the fairy story of Hop o'my Thumb. The Seven Years' War (1756-63) is also the Third Silesian War.