A soft, babyish word for the stomach — the part of your body where food goes. It is a shortened, friendly form of 'tummy', which is itself a child's version of 'stomach'. British English much more than American. You hear it from parents talking to small children ('Is your tum sore?'), and you hear adults use it about themselves in a light, joking way, usually about eating too much or about a soft belly: 'a bit of a tum'. It is never used in a doctor's office, in writing, or in any serious situation — if you say 'the pain is in my tum' to a doctor, it will sound like you are pretending to be four years old. Slightly old-fashioned even in Britain; 'tummy' is far more common, and 'tum' has a cosy, nursery feeling to it.