The study of the structure of words and their parts is called morphology.
Morphology examines how words are built from morphemes, the smallest units that carry meaning or grammatical function. In “catching,” for example, “catch” is a lexical root and “-ing” contributes grammatical meaning. Morphemes may stand alone, like “book,” or be bound forms that cannot normally appear independently, like many prefixes and suffixes.
The field covers both word formation and inflection. Derivation creates related words, as “happy” becomes “unhappy” or “happiness,” while inflection changes a word to express features such as number, tense or aspect without necessarily creating a new dictionary entry. Morphology sits between phonology, which studies sound patterns, and syntax, which studies how words combine into phrases and sentences. The term entered modern linguistic usage through August Schleicher in 1859, although systematic word analysis is much older, including Pāṇini’s detailed Sanskrit grammar.