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Webster 1828 Edition

, n.

A mild or moderate heat.

Indifference; want of zeal or ardor; coldness.

The defect of zeal is lukewarmness, or coldness in religion.

lukewarmness ‎(countable and uncountable, plural lukewarmnesses)

The property of being lukewarm; ambivalence, weakness.
- 2012, Christopher Clark, The Sleepwalkers, Penguin 2013, p. 343:
  Sazonov was furious at the lukewarmness of the British and French reactions to Russia's protests.