The antonyms for the phrase "was suitable" are manifold, as it implies that something is appropriate, fitting, or eligible for a specific purpose or task. Thus, words that could be considered antonyms, depending on their context and usage, include unsuitable, inappropriate, unfitting, inadequate, or incompatible, among others. These terms suggest that whatever was being described as suitable is, in fact, not the right match for the intended function or user. Therefore, a different approach or option might be needed instead. Choosing the right antonym for "was suitable" depends on the context and the meaning that the speaker or writer intends to convey.