theory (http://www.etymonline.com/index.php?allowed_in_frame=0&search=theory&searchmode=none)
1590s, "conception, mental scheme," from L.L. theoria (Jerome), from Gk. theoria "contemplation, speculation, a looking at, things looked at," from theorein "to consider, speculate, look at," from theoros "spectator," from thea "a view" + horan "to see" (see warrant). Sense of "principles or methods of a science or art (rather than its practice)" is first recorded 1610s. That of "an explanation based on observation and reasoning" is from 1630s.
science (http://www.etymonline.com/index.php?allowed_in_frame=0&search=science&searchmode=none)
c.1300, "knowledge (of something) acquired by study," also "a particular branch of knowledge," from O.Fr. science, from L. scientia "knowledge," from sciens (gen. scientis), prp. of scire "to know," probably originally "to separate one thing from another, to distinguish," related to scindere "to cut, divide," from PIE root *skei- (cf. Gk. skhizein "to split, rend, cleave," Goth. skaidan, O.E. sceadan "to divide, separate;" see shed (v.)). Modern sense of "non-arts studies" is attested from 1670s. The distinction is commonly understood as between theoretical truth (Gk. episteme) and methods for effecting practical results (tekhne), but science sometimes is used for practical applications and art for applications of skill. Main modern (restricted) sense of "body of regular or methodical observations or propositions ... concerning any subject or speculation" is attested from 1725; in 17c.-18c. this concept commonly was called philosophy. To blind (someone) with science "confuse by the use of big words or complex explanations" is attested from 1937, originally noted as a phrase from Australia and New Zealand.