Internal reconstructionInternal reconstruction is a method of reconstructing an earlier state in a language's history using only language-internal evidence of the language in question. The comparative method compares variations between languages, such as in sets of cognates, under the assumption that they descend from a single proto-language, but internal reconstruction compares variant forms within a single language under the assumption that they descend from a single, regular form. For example, they could take the form of allomorphs of the same morpheme.
LexicologyLexicology is the branch of linguistics that analyzes the lexicon of a specific language. A word is the smallest meaningful unit of a language that can stand on its own, and is made up of small components called morphemes and even smaller elements known as phonemes, or distinguishing sounds. Lexicology examines every feature of a word – including formation, spelling, origin, usage, and definition. Lexicology also considers the relationships that exist between words.
Semantic changeSemantic change (also semantic shift, semantic progression, semantic development, or semantic drift) is a form of language change regarding the evolution of word usage—usually to the point that the modern meaning is radically different from the original usage. In diachronic (or historical) linguistics, semantic change is a change in one of the meanings of a word. Every word has a variety of senses and connotations, which can be added, removed, or altered over time, often to the extent that cognates across space and time have very different meanings.