the fact that you no longer have something or have less of something
He suffered a gradual loss of memory.
At a loss
not to know what to do or say
I’m at a loss to know how I can help you.
to no longer have something because you do not know where it is
I’ve lost my ticket.
not knowing where you are and how to get to a place
I got lost in the New York subway system.
to explain something in a way that is not clear to (someone) : to confuse (someone)
I’m sorry. You’ve lost me.
Lose it (informal)
to stop being able to control your emotions and suddenly start to shout, cry, or laugh
I’d been trying so hard to stay calm but in the end I just lost it.