'libertarian-leaning' is a compound formed from 'libertarian' + 'leaning'. 'Libertarian' relates to 'liberty' and was formed to denote supporters of greater individual freedom; 'leaning' is the present participle of 'lean', meaning an inclination or tendency.

'Libertarian' derives from formations based on 'liberty' (Latin 'libertas' → Old French 'liberté' → Middle English 'liberte') and the suffix '-arian' (used to form nouns/adjectives). The modern adjective/noun 'libertarian' emerged in the 19th century (from French 'libertaire' and later English usage). 'Lean' comes from Old English 'hlinian' meaning 'to incline'. The compound 'libertarian-leaning' developed in modern political English by combining these elements to describe a tendency toward libertarian views.

Initially, 'libertarian' referred broadly to matters of liberty and those advocating liberty; 'leaning' originally meant a physical slope or inclination. Over time, the combined phrase evolved to mean a figurative inclination toward libertarian political beliefs.