interchangeably

from WordNet (r) 3.0 (2006)

interchangeably
    adv 1: in an interchangeable manner; "these terms can be used
           interchangeably"

from The Collaborative International Dictionary of English v.0.48

Interchangeable \In`ter*change"a*ble\, a. [Cf. OF.
   entrechangeable.]
   [1913 Webster]
   1. Admitting of exchange or mutual substitution.
      "Interchangeable warrants." --Bacon.
      [1913 Webster]

   2. Following each other in alternate succession; as, the four
      interchangeable seasons. --Holder. --
      {In`ter*change"a*ble*ness}, n. -- {In`ter*change"a*bly},
      adv.
      [1913 Webster]

from Bouvier's Law Dictionary, Revised 6th Ed (1856)

INTERCHANGEABLY. Formerly when deeds of land were made, where there Were 
covenants to be performed on both sides, it was usual to make two deeds 
exactly similar to each other, and to exchange them; in the attesting 
clause, the words, In witness whereof the parties have hereunto 
interchangeably set their hands," &c., were constantly inserted, and the 
practice has continued, although the deed is, in most cases, signed by the 
grantor only. 7 Penn. St. Rep. 320.