'cation-mediated' is a modern scientific compound formed by combining 'cation' and 'mediated'. 'Cation' is used in chemistry to denote a positively charged ion; 'mediated' is the past-participle adjective from 'mediate'.

'cation' entered chemical vocabulary in the 19th century from Greek-derived coinages used in electrochemistry, while 'mediate' comes from Latin 'mediatus' (from 'medius' meaning 'middle'); the compound 'cation-mediated' arose in 20th-century scientific English to describe processes occurring via cations.

Individually, 'cation' denotes a positive ion and 'mediate' means 'to act as an intermediary'; combined, the compound specifically means 'caused or facilitated via positive ions' and retains those component senses in technical usage.