intensen

From intense +‎ -en.

intensen (third-person singular simple present intensens, present participle intensening, simple past and past participle intensened)

1. (intransitive, rare) To grow or become more intense; intensify
   • 1973, The School Counselor, volume 21, page 142:

     By the last trip, suddenly and almost without my being aware of it, the sea becomes its own lure: a refreshing break from the intensening heat of August.

   • 2011, Ricky Spain, Jr., The Protectors, page 120:

     As the fight intensened the sky seemed to turn an orange-yellow and black smoke rose into the air.

   • 2016, John Lewis-Stempel, Where Poppies Blow:

     Punctually as we stand-to about 3 a.m. hark! and their thin sweet voice intensening with the growing light 'droppeth as the gentle rain from Heaven upon the place beneath'.