'straight-line-based' originates from Modern English, specifically a compound of the words 'straight', 'line', and 'based', where 'straight' meant 'not curved', 'line' meant 'a long narrow mark or path', and 'based' meant 'having a base or foundation'.

'straight' comes from Old English 'streht' (related to 'stretched') meaning 'straight or extended'; 'line' comes via Old French from Latin 'linea' meaning 'linen thread, line'; 'base' derives from Old French 'base' from Latin 'basis' meaning 'foundation'. The compound form developed in modern technical and descriptive English to denote things founded on straight-line assumptions.

Initially the component words referred to physical straightness and foundations; over time the compound evolved to describe methods, models, or descriptions that specifically rely on straight-line (linear) assumptions rather than curved or nonlinear approaches.