This is one of those words that some readers/listeners will come across and think “WTF mate?” I shall expound all for you now!
puissance (n.) IPA Pronunciation: 
power, might, force
ARCHBISHOP OF YORK
That he should draw his several strengths together
And come against us in full puissance,
Need not be dreaded.
– Henry IV, Part 2 (I.iii)
This word is most commonly used in reference to military power, but it can be applied elsewhere as well. The pronunciation depends on the line of text. The word can be two syllables by, or can be three if the line of verse doesn’t scan out to 10 syllables without it. Some pronounce the first syllable “pyoo” some “pwee,” I’ve seen it both ways in dictionaries – sometimes both ways in the same dictionary. It sounds funny no matter how you say it so pick one.