法医学は legal medicine もしくは forensic medicine ですが,この由来を調べてみました.
まずは,forensicの意味は,
fo·ren·sic [fuh-ren-sik] adjective 1. pertaining to, connected with, or used in courts of law or public discussion and debate.
Origin: 1650–60; < Latin forēns ( is ) of, belonging to the forum, public (see forum, -ensis) + ic
接尾辞の意味は,
-ensis a Latin adjectival suffix meaning “pertaining to,” “originating in,” used in modern Latin scientific coinages, especially derivatives of placenames: canadensis; carolinensis.
ということで,「法(forum)に関する(ensis -> ensic) 医学(medicine)」というのが語源みたいです.