1. Transmitting light; able to be seen through with clarity
   "crystal clear skies"
   - crystalline, limpid, lucid, pellucid, transparent 
2. (of language) transparently clear; easily understandable
   "a crystal clear explanation"
   - limpid, lucid, luculent, pellucid, perspicuous

See also: clear

• smooth muscle cell
• smooth out
• smooth over
• smooth plane
• smooth snake
• smooth softshell
• smooth sumac
• smooth winterberry holly
• smooth woodsia
• smooth-bodied
• smooth-faced
• smooth-haired
• smooth-haired fox terrier
• smooth-leaved elm
• smooth-shaven
• smooth-shelled
• smooth-skinned
• smooth-spoken
• smooth-textured
• smooth-tongued
• smoothbark
• smoothbore
• smoothed
• smoothen
• smoothened