'functional-structural' is a compound combining 'functional' and 'structural'. 'functional' ultimately originates from Latin 'functio' (from 'fungi') meaning 'to perform' or 'to execute', and 'structural' originates from Latin 'structura' (from 'struere') meaning 'to build, pile up'.

The element 'functional' came into English via Medieval/Latin 'functio' and Old French forms before developing into the adjective 'functional'. 'Structural' derives from Latin 'structura' and French 'structure', entering English as 'structure' and later forming the adjective 'structural'. The compound form combines these two modern English adjectives.

Individually, 'functional' originally focused on performance or role and 'structural' on physical or organizational make-up; combined, the compound has come to denote concern with both how something works and how it is constituted or organized.