'hypoacidity' originates from Greek and Latin elements: the Greek prefix 'hypo-' (ὑπό) meaning 'under, less than' combined with the element 'acidity' ultimately from Latin 'acidus' meaning 'sour/acid'.

'hypo-' (Greek) wasattached to English medical and scientific nouns (like 'acidity') in modern English usage; 'acidity' comes from Old French/Latin via Middle English from Latin 'acidus', and the compound 'hypoacidity' developed in modern scientific/medical English to denote reduced acidity.

Initially a literal combination meaning 'under/smaller acidity', it became a technical term used especially in medicine to denote reduced gastric acid secretion (and more generally low acidity).