Pronunciation: ' be-s ə l-
Function: noun
Etymology: Friedrich W. Bessel † 1846 Prussian astronomer
Date: 1872
: one of a class of transcendental functions expressible as infinite series and occurring in the solution of the differential equation x 2 ( d 2 y / dx 2 ) + x ( dy / dx ) = ( n 2 - x 2 ) y