The Collaborative International Dictionary of English v.0.48:
Behalf \Be*half"\, n. [OE. on-behalve in the name of, bihalven
by the side of, fr. AS. healf half, also side, part: akin to
G. halb half, halber on account of. See Be-, and Half,
Advantage; favor; stead; benefit; interest; profit; support;
In behalf of his mistress's beauty. --Sir P.
Against whom he had contracted some prejudice in behalf
of his nation. --Clarendon.
In behalf of, in the interest of.
On behalf of, on account of; on the part of.