1. 参军,入伍;联合起来：join in 参加(活动) | join up 参军,入伍;联合起来 | play a joke on sb. 开某人的玩笑

2. 联合起来,联结起来：join in 参加,加入 | join up 联合起来,联结起来 | just now 现在,眼下;刚才

3. 联合：26.break a way from摆脱; | 27.join up联合; | 28.be against反对;

4. 连接起来：hurry up赶快 | join up连接起来 | pick up拾起;学会;用车来接;收听到

1. 参军；入伍
If someone joins up, they become a member of the army, the navy, or the air force.

e.g. When hostilities broke out he returned to England and joined up.
战事爆发之后，他回到英格兰参军了。

2. （与…）联合；（与…）会合；（与…）组成联盟
If one person or organization joins up with another, they start doing something together.

e.g. Hawkins joined up with Mick in Malaga, and the two went touring around the countryside...
霍金斯在马拉加和米克会合，然后两个人到乡间游玩去了。
e.g. Councils are joining up with their European counterparts...
这些委员会将与欧洲的委员会结成联盟。