(n.) A plane figure having ten sides and ten angles\; any figure having ten angles. A regular decagon is one that has all its sides and angles equal.

Big Dick Decalogue Ten Commandments X abundant year academic year annum bissextile year calendar month calendar year century common year day decagon decagram decahedron decaliter decameter decare decastere decastyle decasyllable decemvir decemvirate decennary decennium decigram deciliter decimeter decurion defective year fiscal year fortnight hour leap year lunar month lunar year lunation luster lustrum man-hour microsecond millennium millisecond minute moment month moon quarter quinquennium regular year second semester session sidereal year solar year sun ten tenner term trimester twelvemonth week weekday year