To require or want something or to experience a deficiency: What this laboratory lacks is a new microscope because there are only old ones which don't work properly.

1. Not firm, relaxed, or negligent: Both parents were lax with their supervision of the children and, as a result, the children often got into mischief.
2. Not strict enough: Shanna's university has been lax about enforcing the rules in the dormitories about making so much noise after a specified time.