The term "on-course" typically implies that one is moving towards their intended destination or goal. However, its antonyms could refer to a deviation or diversion from the intended path. These could include words such as off-course, off-track, off-road or wayward. Other antonyms could also be words that suggest stagnation or inaction, such as idle, dormant or stationary, which indicate a lack of progress towards a goal. Alternatively, antonyms could also be words that suggest going backwards or undoing progress, such as regressing, reversing or backtracking. In conclusion, antonyms for "on-course" could include words that suggest deviation, inaction or regression.