1 PHRASAL VERB 坐起来;坐直 If you sit up, you move into a sitting position when you have been leaning back or lying down. 坐起来;坐直 [Also VERB PREPOSITION n (not pron)]
2 PHRASAL VERB 使…坐起身来;让…直起身子 If you sit someone up, you move them into a sitting position when they have been leaning back or lying down. 使…坐起身来;让…直起身子 [Also VERB PREPOSITION n (not pron)]
3 PHRASAL VERB 深夜未睡;熬夜 If you sit up, you do not go to bed although it is very late. 深夜未睡;熬夜
SYN stay up, stay awake, not go to bed
4 PHRASAL VERB 突然关注;警觉 If something makes you sit up, it makes you suddenly pay attention to what is happening. 突然关注;警觉