'proclamatory' originates from Latin, specifically the word 'proclamatorius' (from 'proclamare'), where 'pro-' meant 'forth' and 'clamare' meant 'to cry out' or 'call'.

'proclamatory' changed from Latin 'proclamatorius' (Medieval/Church Latin) into early Modern English forms (e.g. 'proclamatory'/'proclamatorie') and eventually became the modern English adjective 'proclamatory'.

Initially it meant 'serving to cry out publicly' or 'used in making a public call', but over time it evolved to mean 'relating to or expressing a formal announcement or declaration', and also acquired a sense of being ostentatiously declarative.