overharden

From over- +‎ harden.

overharden (third-person singular simple present overhardens, present participle overhardening, simple past and past participle overhardened)

1. To harden too much.
   • 1661, Robert Boyle, “[Some Specimens of an Attempt to Make Chymical Experiments Useful to Illustrate the Notions of the Corpuscular Philosophy.] The History of Fluidity and Firmnesse. The Second Part. Of Firmnesse.”, in Certain Physiological Essays and Other Tracts; […], 2nd edition, London: […] Henry Herringman […], published 1668, →OCLC, page 286:

     [I]t has acquir'd ſuch a hardneſs, that being throvvn againſt the floor it vvould rebound, and vvas brittle like over-harden'd Steel.

     An adjective use.

• “overharden”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.