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Webster 1913 Edition

Adj.

[L.

inexcitabilis

from which one cannot be aroused. See

not, and

Not susceptible of excitement; dull; lifeless; torpid.

Adj.

[in and excitable.] Not susceptible of excitement; dull; lifeless; torpid.

inexcitable ‎(comparative more inexcitable, superlative most inexcitable)

Not excitable.
- (Can we date this quote?), Wilkie Collins, I Say No:
  Even the inexcitable old doctor had felt the attraction which had already conquered three such dissimilar people as Alban Morris, Cecilia Wyvil, and Francine de Sor. He was thinking of Emily.