unthankful a not feeling or showing gratitude Usage(s) But with the great rousing hosannas, and the last powerful words of the "Agnus Dei" no one was likely to go home uninspired or unthankful. But let us not be unthankful for small things. Because I believe the people were ungrateful and unthankful to God and were not a praying people. Synonym(s) ungrateful thankless Antonym(s) grateful