Etymology

[Dave Paprocki]

That branch of philological science which treats of the
history of words, tracing out their origin, primitive significance, and
changes of form and meaning.

[Marquetta]

I am surprised that this word is not here yet....now it is.
[Etymology] is the study of the [origins of words]. Some words have been derived from other languages, possibly in a changed form (the source words are called etymons). Through old texts and comparisons with other languages, etymologists try to reconstruct the history of words — when they entered a language, from what source, and how their form and meaning changed.
A word often misused and mispronounced entymology which is the study of [insects]!

[Britney]

The study of the origin of words and the way in which their meanings have changed throughout history.