'light-absorbing' originates from Modern English as a compound of 'light' and the present participle 'absorbing' (formed from the verb 'absorb').

'absorbing' comes from Latin 'absorbere' (ad- + sorbere/sorbēre), passed into Old French as 'absorber' and into Middle English as 'absorben/absorben', eventually becoming the modern English verb 'absorb'. 'light' comes from Old English 'lēoht' (or 'leoht') and developed into the modern English 'light'.

Initially, the verb 'absorb' meant 'to suck in or take up (a substance or force)'; over time it retained that core sense and extended to contexts like light or energy. The compound 'light-absorbing' therefore developed to mean 'taking in light' and has kept that literal sense.