Learner's definition of SOURCE
1 : someone or something that provides what is wanted or needed
The college had its own power source.
a water source = a source of water
She has been a great source of strength to me.
His job is the family's main source of income.
2 : the cause of something (such as a problem)— usually + of 3 : a person, book, etc., that gives information
A government source spoke to the press today.
The reporter has refused to reveal his sources.
According to one source, the program will not cost a lot.
information from various intelligence sources
a reference source
4 : the beginning of a stream or river of water