Impossible to replace: irreplaceable antiques. (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 "irreplaceable" in a sentence
""In his case, the word 'irreplaceable' has real substance.""
"On her tour Zweiger met her guests downstairs and pointed out the old confessionals, the majolica Stations of the Cross along the side walls, which she described as irreplaceable as are so many of the artifacts in the church."
"Rossi and other researchers, however, said that embryonic stem cells are still crucial because, among other things, they remain irreplaceable for evaluating alternatives."