'rhyolitic' originates from Greek via Neo-Latin and German, specifically from the word 'rhyolite' (derived from Greek 'ῥυάξ' 'rhyax' meaning 'stream' and 'λίθος' 'lithos' meaning 'stone'), with the adjective-forming suffix '-ic'.

'rhyax' changed into Neo-Latin and German forms (e.g. Neo-Latin/German 'rhyolith'/'Rhyolith'), which entered English as 'rhyolite', and the modern adjective 'rhyolitic' was formed from that noun.

Initially connected etymologically to the idea of a 'stream' or 'flow' in Greek and referred to the rock 'rhyolite'; over time the meaning specialized to 'of or relating to rhyolite' (i.e., describing composition or texture).