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Webster 1913 Edition

Noun.

The act of kindling or the state of being kindled; ignition.

Locke.

Noun.

The act of kindling or setting on fire; or the state of being kindled; inflammation.

accension ‎(plural accensions)

(obsolete) The act of kindling or the state of being kindled; ignition.
- 1646, Thomas Browne, Pseudodoxia Epidemica, II.5:
  From Small-coal ensueth the black colour and quick accension; for neither Brimstone nor Petre, although in Powder, will take fire like Small-coal [...].