On the spot is a commonly used phrase to indicate something done immediately or at that moment. However, there are many synonyms for the term that can be used in different contexts. 'At once,' 'instantly,' 'immediately,' 'straight away,' and 'right away' are some synonyms that suggest immediate action. Similarly, 'spontaneously,' 'impromptu,' and 'ad lib' denote an action or decision taken without pre-planning. Other synonyms to convey urgency or the pressure to take immediate action include 'at a moment's notice,' 'lickety-split,' and 'pronto.' Whether used in a professional or personal context, having a versatile vocabulary can help communicate ideas more effectively.