1. natural environment; nutrient setting for microorganism.   propellant   solvent   perigee   medium   Hint Half-n-half Clue   2. tendency to drive back or distaste.   stratum   vise   velocity   repulsion   Half-n-half Clue   3. quantity that can be defined or that can limit.   parameter   log   pachyderm   touchstone   Half-n-half Clue   4. flying reptile now extinct.   orifice   pachyderm   summation   pterodactyl   Half-n-half Clue   5. change of form, character or circumstances.   sextant   uniformity   projectile   metamorphosis   Half-n-half Clue   6. substance or liquid that dissolves solute.   transition   solstice   kaleidoscope   solvent   Half-n-half Clue   7. vertebrate animal whose female suckles the young.   magnitude   mammal   quagmire   turbulence   Half-n-half Clue