a Jewish festival celebrated on the 18th day of Iyar, being the 33rd day of the Omer, traditionally in commemoration of the end of the plague that killed Rabbi Akiba's students or of the bravery of Bar Kokba.
Origin: 1900–05; < Heb lagh bāʿōmer, equiv. to lagh 33rd + bā, var. of bə in + ʿōmerOmer
[lahg boh-mer, buh-oh-mer] 
