1. To allow a period of time to pass or be spent idly or without notice. A noun or pronoun is used between "slip" and "away." I don't want to let the whole summer slip away without going anywhere nice for a vacation. Sorry, I got distracted playing my game and ended up letting the afternoon slip away.

2. To allow someone or something that one desires leave or be taken from one, especially due to negligence or inattentiveness. A noun or pronoun is used between "slip" and "away." I let you slip away from me once before in my life, and I've never stopped regretting it. I won't let that happen again.

3. To fail to capitalize on some opportunity. A noun or pronoun is used between "slip" and "away." What are you waiting for, call them back! Don't let such an amazing chance slip away!