To be without, to need, to require.

“My life lacks excitement.”

To be short (of or for something).

“He'll never lack for company while he's got all that money.”

To be in want.

The absence of something; a lack.

Missing or not having enough of (a good quality, etc).

“This cheese is lacking in pungency.”

Not carrying a firearm.

“Are you packing or lacking?”