verb

• (transitive) To make brighter or clearer; to illuminate.
  "to lighten an apartment with lamps or gas; to lighten the streets"
• (intransitive) To become brighter or clearer; to brighten.
• (intransitive, now rare) To flash lightning, to give off lightning.
  "Enter the Conjurer; it lightens and thunders […]"
• (transitive) To emit or disclose in, or as if in, lightning; to flash out, like lightning.
  "[…] behold his eye, As bright as is the eagle’s, lightens forth Controlling majesty:"

verb

• (transitive) To alleviate; to reduce the burden of.
  "Sorrow can be lightened by being openly brought out."
• (transitive) To make light or lighter in weight.
• (transitive) To make less serious or more cheerful.
  "They looked unto him, were lightened: and their faces were not ashamed."
• (intransitive) To become light or lighter in weight.