'aquo-pentamminecobaltic' is a compound technical term formed from several classical roots: 'aquo-' from Latin 'aqua' meaning 'water'; 'penta-' from Greek 'penta' meaning 'five'; 'ammine' from Neo-Latin 'ammonia' (referring to ammonia ligands); and 'cobaltic' from 'cobalt' (element name) with the adjectival suffix '-ic' indicating relation to cobalt.

The component-based naming arose with the development of coordination-chemistry nomenclature (late 19th–early 20th century, e.g., work by Alfred Werner). Systematic names such as 'pentaamminoaquacobalt(III)' and older hyphenated forms like 'aquo-pentamminecobaltic' reflect attempts to indicate ligand types and counts; these evolved into the modern IUPAC-style formulæ and names for coordination complexes.

Initially each morpheme simply named a ligand type or atom ('aqua' = water, 'penta-' = five, 'ammine' = ammonia ligand, 'cobalt(ic)' = relating to cobalt). Over time the assembled term became a fixed technical label for the specific cobalt(III) species [Co(NH3)5(H2O)]3+ and for adjectives describing that species.