Longman Dictionary of Contemporary English - imagination

~ n 1 the ability to form pictures or ideas in your mind  (Children often have very vivid imaginations. | With a little imagination, he could visualize the old house as a luxury hotel.) 2 something that is caused only by your mind, and does not really exist or did not really happen  (Did you hear that noise, or was it my imagination?) 3 in your imagination only existing or happening in your mind, not in real life  (The difficulties are all in your imagination.) 4 capture/catch sb's imagination to make people feel very interested and excited  (His music captured the imagination of a whole generation of young people.) 5 leave sth to sb's imagination to deliberately not describe something because you think someone can guess or imagine it  (I'll leave the details of the affair to your imagination.) 6 use your imagination! spoken used to tell someone that they can easily guess the answer to a question, so you should not need to tell them  (- see also not by any stretch of the imagination stretch2 (5))