'Reactive' definitions:

Definition of 'reactive'

From: WordNet
adjective
Participating readily in reactions; "sodium is a reactive metal"; "free radicals are very reactive" [ant: unreactive]
adjective
Reacting to a stimulus; "the skin of old persons is less reactive than that of younger persons" [syn: reactive, responsive]

Definition of 'Reactive'

From: GCIDE
  • Reactive \Re*act"ive\ (r[-e]*[a^]kt"[i^]v), a. [Cf. F. r['e]actif.] Having power to react; tending to reaction; of the nature of reaction. -- {Re*act"ive*ly}, adv. -- {Re*act"ive*ness}, n. [1913 Webster]