A self-evident truth. See Synonyms at cliché.(noun)
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 "truism" in a sentence
"Unfortunately, it has come to a point that a good test of a political "truism" is that, if a partisan Republican running for or holding office proclaims it, it is probably not true."
"And, we realized the old truism from the original cytogenetics which was that the telomere is really important for protecting ends and, as you might expect, the cell actually devotes all sorts of machinery to make sure that never goes wrong, or goes wrong as little as possible."
"The truism is that "correlation is not causation.""