Here is a word whose meaning and pronunciation both eluded me. It means "of great force or vigor: strong, powerful. and it is pronounced PUISSant.
Puissant has some powerful ties to some more commonplace English words. Although puissant has a considerably fancier feel than power and potent, all three words share the same Latin ancestor: posse, a verb meaning "to be able." (English posse, meaning "a group of people sharing some common interest," is also related to the Latin verb but came into the language via the Medieval Latin phrase posse comitatus, literally "power of the county.") Potent came from potent-, potens, a present participle of posse. Power came to us by way of Anglo-French poer, which itself comes from a Vulgar Latin alteration of posse. From poer also came the Anglo-French adjective pussant, meaning "able" or "powerful," and English speakers borrowed that to form puissant in the 15th century.