Definition of lightens:
(v) :
(transitive) To alleviate; to reduce the burden of.
(v) :
(transitive) To make less serious or more cheerful.
(v) :
(transitive) To make brighter or clearer; to illuminate.
(v) :
(intransitive) To become brighter or clearer; to brighten.
(v) :
(transitive) To make light or lighter in weight.
(v) :
(intransitive) To become light or lighter in weight.