prescription (n.) Look up prescription at Dictionary.com
late 14c., in law, "the right to something through long use," from Old French prescription (13c.) and directly from Latin praescriptionem (nominative praescriptio) "a writing before, order, direction," noun of action from past participle stem of praescribere "write before, prefix in writing; ordain, determine in advance," from prae "before" (see pre-) + scribere "to write" (from PIE root *skribh- "to cut"). Medical sense of "written directions from a doctor" first recorded 1570s.