'declaim' originates from Latin, specifically the word 'declamare', where 'de-' functioned as an intensive prefix and 'clamare' meant 'to cry out, shout'.

'declaim' passed into Modern English via French 'déclamer' and Latin 'declamare'; the form and usage were established in Early Modern English from these sources.

Initially, it meant 'to cry out or call loudly', but over time it evolved to mean 'deliver speech or recite in a rhetorical or theatrical manner' in modern usage.