linguistics

[brendagillespie1]

in linguistics what is the study of the form history behaviour and meaning of words

[mazie]

Lexicology

[syruphead]

I would suggest etymology is a better answer to your question

[atalanta]

Could be Philology. It refers to Linguistics.
Etymology is the study of the history and development of words from earlier forms or earlier roots. A dictionary of etymology would explain that "paediatrics" comes from the greek roots for "child" and "doctor"

[syruphead]

Etymology1. That branch of philological science which treats of the history of words, tracing out their origin, primitive significance, and changes of form and meaning.

Seems to have all your question mentions, Brenda