second basen. Baseball 1. The base across the diamond from home plate, to be touched second by a runner.2. The position played by a second baseman.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.sec?ond base? n. 1. the second in order of the bases from home plate in baseball. 2. the position of the player covering the area of the infield between second and first bases. [1835?45, Amer.] sec?ond base?man, n. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.