'varying-pressure' originates from modern English, combining the present-participle form 'varying' (from the verb 'vary') and the noun 'pressure'. 'vary' ultimately originates from Latin, specifically the word 'variare' (via Old French 'varier'), where the root 'var-' meant 'to change' or 'different'. 'pressure' ultimately originates from Latin, specifically the word 'pressura' (via Old French 'pression'), where the root 'premere' meant 'to press.'

'vary' changed from Latin 'variare' to Old French 'varier' and entered Middle English as forms such as 'varien', eventually becoming the modern English verb 'vary'. 'pressure' changed from Latin 'pressura' to Old French 'pression' and Medieval Latin/Old French forms before developing into modern English 'pressure'.

Initially, the components meant 'to change' (for 'vary') and 'the act of pressing' (for 'pressure'); over time the compound has been used in technical and descriptive contexts to mean 'pressure that changes', the combined current meaning.