in·ter·change • v. / ˌintərˈchānj/ [tr.] (of two or more people) exchange (things) with each other: superior and subordinates freely interchange ideas and information. ∎  put each of (two things) in the other's place: the terms are often interchanged. ∎  [intr.] (of a thing) be able to be exchanged with another: diesel units will interchange with the gasoline ones.• n. / ˈintərˌchānj/ 1. the action of interchanging things, esp. information: the interchange of ideas | a free-market interchange of goods and services. ∎  an exchange of words: listening in shock to this venomous interchange.2. alternation: the interchange of woods and meadows.3. a road junction designed on several levels so that traffic streams do not intersect.DERIVATIVES: in·ter·change·a·bil·i·ty / ˌintərˌchānjəˈbilitē/ n.in·ter·change·a·ble adj.in·ter·change·a·ble·ness n.in·ter·change·a·bly / -blē/ adv.

interchange vb. XIV. ME. enterchaunge — OF. entrechangier; see INTER-, CHANGE. Hence as sb. XVI.
So interchangeable (whence interchangeably) XIV. — OF.