'horizontalism' originates from English, formed by adding the suffix '-ism' to 'horizontal', where 'horizontal' comes (via French and Late Latin) from Greek elements related to 'horizon' (from Greek 'hōrizōn', from 'horos' meaning 'boundary').

'horizontal' passed into English from French and Late Latin 'horizontalis', itself from Greek 'hōrizōn' (the present participle of 'hōrizō', 'to divide' or 'to bound'); in modern English the compound 'horizontalism' was later coined by adding the productive noun-forming suffix '-ism' to denote doctrines or tendencies associated with horizontality.

Initially related simply to the idea of being parallel to the horizon or 'flatness', the term evolved to denote abstract doctrines: in social contexts, the preference for non-hierarchical organization; in economics, a specific theory about the elasticity of the monetary supply.