Mum/mʌm/ Definition 1 of 4Pro Tip 1/3Affectionate Term Mum is often used to show affection and cozy familiarity when addressing one's mother. Thanks for the cookies, mum! Pro Tip 2/3British Usage Prefer 'mum' over 'mom' when speaking or writing in British English, it is the UK standard. My mum makes the best roast dinner. Pro Tip 3/3Casual Conversations Use 'mum' in casual or informal language, but choose more formal terms in professional settings. Can you call my mum to let her know?