We find the word "watch" used by our Lord many times:

And he saith to them: My soul is sorrowful even unto death; stay you here, and watch. (Mk 14:34)

And he cometh, and findeth them sleeping. And he saith to Peter: Simon, sleepest thou? couldst thou not watch one hour? Watch ye, and pray that you enter not into temptation. The spirit indeed is willing, but the flesh is weak. (Mk 14:37:38)

Heaven and earth shall pass away, but my word shall not pass away. But of that day or hour no man knoweth, neither the angels in heaven, nor the Son, but the Father. Take ye heed, watch and pray. For ye know not when the time is." (Mk 13: 31-33)

But what exactly does Jesus mean by this word "watch"?