Words and meanings
Lexicology
Lexicology is the general and objective study of words and their meanings.
In some ways, it is the lexical part of philology.
In other ways it is closely related to etymology, phraseology, and semantics.
Lexicography can be said to be the applied part of lexicology, as it studies the use of words.
'Lexicography' is also and is often used to refer to the compilation of a lexicon. Note that lexicographer is a comparatively specific word, referring to someone who writes dictionaries.
See also
Semiotics
Semiotics can be taken as the study of signs and how we relate them to meaning.
Signs in this context are are anything that can be interpreted to have a meaning, including but not limited to sounds, motions, gesture, images.
In a practical sense we often still focus on words, yet the term is used in part to remind you these are far from the only meaning-carriers, even in a lot of everyday situations.
Sign process is sometimes synonym for semiotics,
arguably a more self-explanatory name to those not already deep in the theory.
Sign process is also sometimes a little more specifically meant as a "any process/activity that involves signs, and probably meaning".
Linguistics is mostly about intentional meaning.
You could say that semiology is more about the signs and symbols and more anthropological, while linguistics more about the structure, meaning and meaningful communication.
As such, linguistics courses may skim over semiology, or use the term only for all the inbetweens - analogy, allegory, metonymy, metaphor, symbolism, and also conduct, behaviour, and a lot of other sociology.
It also overlaps with philosophy, relating to structuralism, and more. (see e.g. Saussure)
Entirely unintentional signs include e.g. diagnosis, as a symptom can be a a sign of a medical condition.
See also: