'lowercase-only' originates from English, specifically the words 'lowercase' and 'only', where 'lower' originally meant 'positioned below', 'case' comes from Latin 'capsa' meaning 'box' (used for a type case), and 'only' comes from Old English 'ānlic' meaning 'single/sole'.

'lowercase' developed from the typographic phrase 'lower case' (the box holding the small letters) and became a single word in modern English; 'case' traces to Latin 'capsa' > Old French 'case' > Middle English 'case'. 'Only' evolved from Old English 'ānlic' to Middle English 'onliche' and modern 'only'. The compound 'lowercase-only' is a modern technical/administrative formation combining these elements.

Initially 'lower case' referred to the physical lower box of type; over time it came to denote small letters generically. The compound 'lowercase-only' later emerged to mean 'limited to those small letters' (i.e., only lowercase).