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This article was written in the memory of Roman Ivanovych Ostash, a prominent Ukrainian onomastic researcher, dialectologist and lexicographer, a man with a great heart and moral authority. This article presents the story of his life, scientifi c activity and his contribution to the development of the Ukrainian linguistics. Very rich scientifi c achievements of Roman Ivanovych Ostash have been shown in the context of his cooperation with a number of researchers and academic institutions in Ukraine and abroad. The article has been included in full bibliography of his scientific papers.