From Longman Dictionary of Contemporary Englishoff-keyˌoff-ˈkey adjective 1 APMmusic that is off-key sounds unpleasant because it is played slightly above or below the correct pitch → in tune The band sounded slightly off-key.2 wrong or not suitable for the situation The jokes during the violent action scenes seemed off-key. —off-key adverb Someone upstairs was singing off-key.
Examples from the Corpus
off-key• The lead singer was completely off-key.• Alexia whistled this time, off-key.• He didn't have a good voice but he was never off-key.• Haden sounded just a little off-key about the whole affair.• The woman laughed but in a strangled, off-key kind of way and it struck me that she might be insane.• I skipped through the neighborhood, singing off-key songs.• The recorder came in with an adagio-like slowness and gravity, momentarily wobbled off-key, then recovered. 