freemason (n.) Look up freemason at Dictionary.com
late 14c., originally a traveling guild of masons with a secret code; in the early 17c. they began accepting honorary members and teaching them the secrets and lore, which was continued into or revived in the 17th century and by 1717 had developed into the secret fraternity of affiliated lodges known as Free and Accepted Masons (commonly abbreviated F. and A. M.). The accepted refers to persons admitted to the society but not belonging to the craft.

The exact origin of the free- is a subject of dispute. Some [such as Klein] see a corruption of French frère "brother," from frèremaçon "brother mason;" others say it was because the masons worked on "free-standing" stones; still others see them as "free" from the control of local guilds or lords [OED]. Related: freemasonic.
freemasonry (n.) Look up freemasonry at Dictionary.com
mid-15c., from freemason + -ry.
mason (n.) Look up mason at Dictionary.com
c. 1200, "stoneworker" (as a surname, early 12c.), from Old French masson, maçon "stone mason" (Old North French machun), probaby from Frankish *makjo or some other Germanic source (compare Old High German steinmezzo "stone mason," Modern German Steinmetz, second element related to mahhon "to make;" see make (v.)). But it also might be from, or influenced by, Medieval Latin machio, matio (7c.) which is said by Isidore to be derived from machina (see machine). The medieval word also might be from the root of Latin maceria "wall." Meaning "a Freemason" is attested from early 15c. in Anglo-French.