late 14c., conneccion, "state or fact of being connected," also connexioun (in this spelling from mid-15c.), from Old French connexion, from Latin connexionem (nominative connexio) "a binding or joining together," from *connexare, frequentative of conectere "to fasten together, to tie, join together," from assimilated form of com "together" (see con-) + nectere "to bind, tie" (from PIE root *ned- "to bind, tie").
Spelling shifted from connexion to connection (especially in American English) mid-18c. under influence of connect, abetted by affection, direction, etc. See -xion.
Meaning "act of connecting" is from c. 1600; sense of "anything that connects" is from 1741. As "circle of persons with whom one is brought into more or less intimate relations" is from 1767. Meaning "the meeting of one means of travel with another" is from 1862. Sense of "supplier of narcotics" is attested by 1934.