prime ministern. Abbr. PM1. A chief minister appointed by a ruler.2. The head of the cabinet and often also the chief executive of a parliamentary democracy.prime ministerial adj.prime ministership, prime ministry n.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.prime minister n 1. (Government, Politics & Diplomacy) the head of a parliamentary government 2. (Government, Politics & Diplomacy) the chief minister of a sovereign or a state prime ministership, prime ministry nCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014prime` min?ister n. the head of government and the head of the cabinet in parliamentary systems. [1640?50] prime` min?is?ter?ship`, prime` min?istry, n. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.