sub·son·ic 
(sŭb-sŏnĭk)
(sŭb-sŏnĭk)adj.
1. Of less than audible frequency.
2. Having a speed less than that of sound in a designated medium.
- straight face
- straight-faced
- circumscriptive
- circumsolar
- circumspect
- circumspection
- circumspectly
- circumstance
- circumstantial
- circumstantial evidence
- circumstantiality
- circumstantially
- circumstantiate
- circumstantiation
- circumstellar
- circumterrestrial
- circumvallate
- circumvallation
- circumvent
- circumventer
- circumvention
- circumventive
- circumventor
- circumvolution
- circumvolve