Changing or varying, especially often and without discernible pattern or reason.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "inconstant" in a sentence
"Mark Twain and Will Rogers lived off the foibles of Congressmen who they described as inconstant, untrustworthy, mendacious, venal, etc, etc."
"I have heard him called inconstant of purpose — when he deserted, for the sake of love, the hope of sovereignty, and when he abdicated the protectorship of England, men blamed his infirmity of purpose."
"I know, at last, what the poet meant by that expression, though the word inconstant strikes me as hardly forcible enough."