to use a needle and syringe (= small tube) to put a liquid such as a drug into a person's body

Phil's a diabetic and has to inject himself with insulin every day. 菲尔患有糖尿病，每天都得给自己注射胰岛素。

to introduce something new that is necessary or helpful to a situation or process

A large amount of money will have to be injected into the company if it is to survive. 如果要挽救这家公司就必须注入大量资金。

I tried to inject a little humour into the meeting. 我试图给会议增添些幽默气氛。