late 15c., "to go through searchingly or in detail, run over with careful scrutiny," from Middle English per- "completely" (see per) + use (v.). Meaning "read carefully and critically" is by 1530s, but this could be a separate formation. Meaning "read casually" is from 19c. Related: Perused; perusing. "The formation looks unusual, but it is well supported by similar formations now obsolete, e.g. peract, perplant, perstand, etc." [Century Dictionary].