'variable-pressure' originates from Modern English as a compound of 'variable' and 'pressure'. 'variable' ultimately originates from Latin 'variabilis' (from the verb 'variare') where 'variare' meant 'to change'; 'pressure' ultimately originates from Latin 'pressura' (from the verb 'premere') where 'premere' meant 'to press'.

'variable' entered English via Old French and Middle English from Latin 'variabilis' and related forms; 'pressure' entered English via Old French forms (e.g. 'pression') from Latin 'pressura'. The compound 'variable-pressure' formed in Modern English by combining these two established words to describe changing pressure phenomena.

Individually, 'variable' meant 'liable to change' and 'pressure' meant 'the act of pressing or force per unit area'; combined as 'variable-pressure', the term specifically denotes pressures that change and has retained that technical meaning in modern usage.