Other forms: besetting; besets
Beset means to attack from all sides — an invading army will beset a castle, or you might find yourself beset by a devastating storm.
Beset also has a very different meaning: to decorate or encrust with jewels or other ornamentation. If you are attending a ball, you may choose a gown that is beset with silver sequins, just be careful that you don't end up looking like a giant disco ball.