'metal-framed' is a Modern English compound formed by combining 'metal' + 'frame' with the adjectival/past-participial suffix '-ed' to mean 'having a frame of metal.'

'metal' comes from Old French 'metal', from Latin 'metallum', ultimately from Greek 'metallon' meaning 'mine' or 'metal'; 'frame' comes from Middle English 'frame' (related to Old English/Middle English roots meaning 'to form, construct'), and the suffix '-ed' is used productively in Modern English to form adjectives from nouns or verbs. These elements were combined in modern usage to form the compound adjective 'metal-framed.'

Initially the components referred separately to 'metal' (the material) and 'frame' (a structural support); combined with '-ed' in Modern English they yield the descriptive sense 'constructed with a metal frame,' a straightforward compositional meaning that has remained stable.