1. To lose visibility of, forget about, misplace, or neglect to pay close attention to someone or something. I'm sorry I'm late—we were having so much fun that I completely lost trace of time. I was watching the bird through my binoculars until I lost trace of it in the canopy. The police lost trace of the criminal somewhere in the swamp.

2. To unintentionally decrease frequency of communication with someone over time until no further contact takes place. Unfortunately, I lost trace of my college roommate, so I have no idea how she's doing now. Yeah, I lost trace of Mark after he moved to Thailand.