Base1  —n. 1 a part supporting from beneath or serving as a foundation. B notional support or foundation (power base). 2 principle or starting-point. 3 esp. Mil. Headquarters. 4 main or important ingredient. 5 number in terms of which other numbers or logarithms are expressed. 6 substance capable of combining with an acid to form a salt. 7 baseball etc. Each of the four stations on a pitch. —v. (-sing) 1 (usu. Foll. By on, upon) found or establish (a theory, hope, etc.). 2 station (troops based in malta). [greek basis stepping]