What is the pronunciation key of word pessimistic?

Here's the pronunciation key for "pessimistic", using the International Phonetic Alphabet (IPA):

ˈpɛsɪˈmɪstɪk

Here's a breakdown:

* ˈpɛs: The "p" is pronounced with a slight puff of air, the "e" as in "pet", and the "s" as in "sun".

* ɪˈmɪs: The "i" is short, like in "bit", the "m" is pronounced as normal, the "i" again is short, the "s" is as in "sun", and the stress falls on this syllable.

* tɪk: The "t" is pronounced as normal, the "i" is short, and the "k" is a hard "k" sound.

So, the pronunciation of "pessimistic" is:

* Pes-i-mis-tic

You can find more information about the IPA and how to pronounce specific sounds at websites like the International Phonetic Alphabet website or online dictionaries.