'soft-liner' originates from English, specifically the compound 'soft' + 'liner', where 'soft' meant 'less severe' and 'liner' derived from the usage in 'hard-liner' meaning 'one who takes a particular line (policy)'.

'soft-liner' developed as a contrast to 'hard-liner', a political term that became common in the 20th century; the suffix '-liner' (from 'line' meaning a policy line) combined with 'soft' to form the modern compound.

Initially it meant 'a politician who favored moderate or conciliatory policies' and over time the meaning has remained largely the same, denoting moderation in policy stance.