Etymology

From Srafopedia

Etymology is the study of the history of words - when they entered a language, from what source, and how their form and meaning have changed over time. The word etymology itself comes from the Greek ἔτυμον (étymon, true meaning, from 'etymos' true) and λόγος (lógos, word).

Types of word origins:
Borrowing, i.e. the adoption of loanwords from other languages.
Word formation such as derivation and compounding.
Onomatopoeia and sound symbolism, i.e. the creation of imitative words.

While the origin of newly emerged words is often more or less transparent, it tends to become obscured through time due to:

Sound change: for example, it is not obvious at first sight that English set is related to sit (the former is originally a causative formation of the latter), and even less so that bless is related to blood (the former was originally a derivative with the meaning "to mark with blood", or the like).

Semantic change: English bead originally meant "prayer", and acquired its modern sense through the practice of counting prayers with beads.

The combination of sound change and semantic change often creates etymological connections that are impossible to detect by merely looking at the modern word-forms. For instance, English lord comes from Old English hlāf-weard, meaning literally "bread guard". The components of this compound, in turn, yielded modern English loaf and ward.

Content from Wikipedia (abridged)