The Collaborative International Dictionary of English v.0.48:

Reactance \Re*act"ance\ (r[-e]*[a^]k"tans), n. [React + -ance.]
   (Elec.)
   The influence of a coil of wire upon an alternating current
   passing through it, tending to choke or diminish the current,
   or the similar influence of a condenser; inductive
   resistance. Reactance is measured in ohms. The reactance of a
   circuit is equal to the component of the impressed
   electro-motive force at right angles to the current divided
   by the current, that is, the component of the impedance due
   to the self-inductance or capacity of the circuit.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

reactance
    n 1: opposition to the flow of electric current resulting from
         inductance and capacitance (rather than resistance)