pessimise

verb4

1. •
   To make (something) pessimal or the worst; (in a weaker sense) to make (something, such as a computer program) less efficient.
2. •
   To become pessimal or the worst.

   • Without an effort to integrate the various design disciplines, for instance, individual subsystems (such as the HVAC system) may be optimized, but the system as a whole may be "pessimized." — 2008
3. •
   To take a pessimistic view of; to speak of in a negative or pessimistic way.
4. •
   To think like a pessimist; to believe the worst.

   • The pessimising and desponding tone of the Tory Foreign Minister's correspondence, in the early part of 1859, can hardly be read without a shudder. — 1865