1. defect in eye or lens preventing proper focusing.   homeostasis   decomposition   astigmatism   congruence   Hint Half-n-half Clue   2. drug or treatment preventing infection.   chassis   anesthetic   chameleon   antiseptic   Half-n-half Clue   3. deficiency of red blood corpuscles.   component   converse   corollary   anemia   Half-n-half Clue   4. formal discourse or essay.   dissertation   arboretum   conifer   contagion   Half-n-half Clue   5. druggist or chemist.   apothecary   congruence   dichotomy   cartographer   Half-n-half Clue   6. collection of stars or brilliant personalities.   component   galaxy   cog   chassis   Half-n-half Clue   7. agent to speed up chemical reaction without it changing.   catalyst   effluvium   decomposition   conjecture   Half-n-half Clue