There are many. Here are just a few examples:
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Examples of one syllable words are:aanareboarboreboxcancarcaredodogdoordougheatedgeeighteyefiveforfourgivegogoathihighheightinisitjayjokejoykeepkingkneelatelightlotmemoonmynonotnoteofoneownpoorpotpourquestquitquiteratrestrootroutesinsomesongthrowtotootoottwousevieviewwhatwhenwhoyearyetyouzipzonezoo
One-syllable words are called monosyllables.
All words have at least one syllable. The word "best" has one syllable.
morgue, man, men, more, mad, mare, mike, mash, male, mom, meek
It depends on the word. Some words have one syllable; some have many more.