The Collaborative International Dictionary of English v.0.48:

Reciprocally \Re*cip"ro*cal*ly\ (r[-e]*s[i^]p"r[-o]*kal*l[y^]),
   adv.
   1. In a reciprocal manner; so that each affects the other,
      and is equally affected by it; interchangeably; mutually.
      [1913 Webster]

            These two particles do reciprocally affect each
            other with the same force.            --Bentley.
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   2. (Math.) In the manner of reciprocals.
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   Reciprocally proportional (Arith. & Alg.), proportional, as
      two variable quantities, so that the one shall have a
      constant ratio to the reciprocal of the other.
      [1913 Webster]