There are several definitions for this word:

1) The health profession that links the health sciences with the chemical sciences and it is charged with ensuring the safe and effective use of pharmaceutical drugs.

2) An establishment in which the profession of pharmacy is practiced, that is where medication is prepared and distributed.

3) (North America mostly) An commercial establishment which fills prescriptions and which sells not only medication, but also miscellaneous items such as magazines, cosmetics and candy.

Etymology: From the Greek φάρμακον, meaning "drug," from a Myceneaen Greek word (roughly "pa-ma-ko"), which appears in Linear B script.

Synonyms for the establishment where the practise of pharmacy takes place include drug store and chemist's (the latter is mostly used in the U.K., Australia, Ireland, New Zealand and Hong Kong.

Barber, Katherine, ed. "Pharmacy." Canadian Oxford Dictionary. 2nd edition. Don Mills : Oxford University Press, 2004. Print.

http://en.wikipedia.org/wiki/Pharmacy

Liddell, George Henry & Scott, Robert, eds. "Πάρμακον." A Greek-English Lexicon. Oxford: Clarendon Press, 1996. Print.