Untoward is a formal word that describes something that is improper or inappropriate, or that is adverse or unfavorable.

// The medication is safe and effective, with no known untoward side effects.

// The investigation found that nothing untoward had happened at the event.

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“You might be thinking that the best course of action would be to make sure that any such generative AI is completely unable to spew out any kind of untoward content. Just do whatever ... AI trickery is needed to ensure that the good stuff is emitted and the bad stuff is kept under lock and key. ... The rub is that trying to simultaneously have generative AI that appears to be fluent and capable in composing natural language and yet also can refrain from emitting the bad stuff is a lot harder of a problem than you might assume.” — Lance Eliot, Forbes, 1 May 2023

For centuries, the adjective toward described “forward-moving” youngsters, the kind who showed promise and were open to listening to their elders. The adjective then came to mean amiable or obliging. The opposite of this now-obsolete sense of toward is froward, meaning “disobedient.” Froward has fallen out of common use, but thankfully another toward antonym, untoward, obliged in picking up the slack. In addition to describing people or things that are “difficult to guide, manage, or work with,” untoward today is applied to that which is unfavorable or adverse, as well as to things that are inappropriate or in bad taste.