8 letters · 12 points in Scrabble
adjective (of speed) less than that of sound in a designated medium
originEtymology tree Proto-Indo-European *upó Proto-Italic *supo Latin sub Latin sub-der. English sub- Proto-Indo-European *swenh₂- Proto-Indo-European *swónh₂os Latin sonus Proto-Indo-European *-ikos Proto-Italic *-ikos Latin -icuslbor. Old French -iquebor. Middle English -ik English -ic English sonic English subsonic From sub- + sonic.
Etymology from Wiktionary, CC BY-SA 3.0