The original or earlier form of an inherited or borrowed word, affix, or morpheme either from an earlier period in a language's development, from an ancestral language, or from a foreign language.
Meaning as derived and conveyed thereby: The literal meaning of a term according to its origin, which may differ from its usual meaning when the latter relies on idiomatic conventions that are not conveyed by the term alone (that is, they must be known in other ways, such as experience, training, education, or dictionary lookup).
A spring that is the source of a river.
An abundant source of knowledge, etc.