set off/out        
phrasal verb with set verb uk/set/ us/set/  setting | set
B2 出发,启程
to start a journey
  What time will we have to set off for Grandma's house tomorrow? 我们明天得在什么时候出发去奶奶家? 
 Jenny set off down the road on her new bike. 珍妮骑着新自行车沿着马路出发了。 
 They've just set off on a round-the-world cruise. 他们刚刚出发去环球旅行。 
 - More examples
 - When we heard he was ill, we set off straight away to see him.
 - They set off before dawn.
 - They set off on their desert crossing two days ago.