p’s and q’s n.pl. Idiom. mind or watch one’s p’s and q’s, to pay careful attention to one’s own behavior or affairs; be cautious or discreet. [1770?80; perhaps from some children’s difficulty in distinguishing the two letters] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.