late 14c., from Middle French compact (14c.) or directly from Latin compactus "concentrated," past participle of compingere "to fasten together, construct," from com- "with, together" (see com-) + pangere "to fix, fasten" (see pact). Compact car is 1960. Compact disc is from 1979.
"agreement," 1590s, from Latin compactum "agreement," noun use of neuter past participle of compacisci "come to agreement," from com- "together" (see com-) + pacisci "to covenant, contract" (see pact).