The term "subject of thought" can be replaced with a variety of other words that convey a similar meaning. One such word is "topic," which refers to the subject matter of a discussion or conversation. Another synonym is "issue," which also refers to a topic or subject, but often implies a controversial or problematic aspect. "Theme" is another option that is commonly used in the context of literature, music, or art to refer to the underlying message or idea. Other synonyms for "subject of thought" include "matter," "content," "focus," "subject matter," and "subject area." Each of these words can be used interchangeably to refer to the main subject or idea that is being considered or discussed.