1. (of gas or air) of less density.   iridescent   noxious   rarefied   volatile   Hint Half-n-half Clue   2. with only one color.   monochromatic   seminal   obtuse   tertiary   Half-n-half Clue   3. pertaining to earthquakes.   septic   prophylactic   unique   seismic   Half-n-half Clue   4. pertaining to memory or memory-aid.   partial   somatic   putrid   mnemonic   Half-n-half Clue   5. formed into layers or divided into classes.   vitriolic   stratified   static   multiform   Half-n-half Clue   6. superfluous or excessive.   saccharine   redundant   somatic   seismic   Half-n-half Clue   7. marked with ridges or parallel grooves on surface.   prehensile   resonant   striated   saline   Half-n-half Clue