The term 'on topic' can be defined by three crossword solutions: THEMATIC (8 letters), GERMANE (7 letters), and APT (3 letters). THEMATIC refers to something that is related to the main subject or theme of a discussion, while GERMANE means relevant or pertinent to the matter at hand. APT, on the other hand, implies being suitable or appropriate for a particular situation. All three words are used to describe something that is on topic and relevant to the conversation.