Speed Beneath the Sound Barrier
This page is the CodyCross answer for the clue below from A Sweet Life, Group 1089, Puzzle 1 (Strawberry Sundae).
Question is: Speed Beneath the Sound Barrier
and the answer is: SUBSONIC
Word Meaning:
SUBSONIC — (of a sound, scientific) having a frequency too low to be audible
Definitions from Wiktionary.