Which word describes a quality that is not immediately obvious or is hidden?

The correct choice conveys a quality that is not immediately obvious or is hidden is "subtle." This word refers to nuances or distinctions that may be difficult to notice or perceive right away. When something is described as subtle, it implies that there are intricacies or underlying features that require careful observation or deeper thinking to appreciate fully.

In contrast, options like "apparent," "ostensible," and "obvious" suggest clarity and visibility, or that something is readily observable. These terms denote a quality that can be easily recognized or understood without the need for close examination, which is the opposite of what is meant by describing something as subtle.