fləˈjelə̇n noun
( -s )
Etymology: flagell um + -in
: a polymeric protein that is the chief constituent of bacterial flagella, that forms helical chains around the hollow core of the flagellar filament, that determines the specificity of the flagellum in eliciting an immune response by its amino acid sequence, and that within any one serogroup exhibits one of two antigenic states determined by the expression of one or the other of two different genes