'internally-supported' is a compound formed in modern English from 'internally' + 'supported'. 'Internally' derives from Latin 'internus' meaning 'inward' or 'inside', and 'supported' comes from Latin 'supportare' (via Old French), meaning 'to carry from below' or 'to hold up'.

'internally' developed from Latin 'internus' → Old/Middle French and Late Latin influence → Middle English 'internal' with the adverbial suffix '-ly'; 'support' comes from Latin 'supportare' → Old French 'soutenir'/'supporter' → Middle English 'supporten', whose past participle produced 'supported'. The modern compound 'internally-supported' is a straightforward adjectival combination in modern English.

Individually, 'internal' originally meant 'inward' and 'support' originally meant 'to carry or hold up'. Together as 'internally-supported' the phrase came to mean 'held up or reinforced from the inside' — a literal technical usage that has remained stable in engineering and descriptive contexts.