Sextant (sex) Noun Def.A sixth of a circle ;an instrument used to determine the position of a ship or an airplane by measuring the positions of the stars Yesterday night, on the ship, I saw a beautiful sight through the sextant.
Septennial(sept) Adjective Def.Lasting for seven year years;happening once every seven years Teachers had a septennial meeting today discussing about the school supplies.l
Septet(sept) Noun Def.A group of seven singers or musicians who perform together;piece of music that is meant to be performed by seven people Last night, I saw a musical by my favorite septet.
Octave(Oct) Noun Def.A group of eight, such as eight lines or eight musical notes My friends wanted to listen to a song that was one octave higher than the song that they just listened.