him is an old Indoeuropean word meaning cold or frost. Possibly from the root ansh to distribute, one gets anshu, a filament or ray. The `frosty rayed' one is usually the moon.
mandar is Erythrina Indica, one of the five heavenly trees. See
http://www.hktree.com/tree/Indian_Coral_Tree.htm for pictures. The root mand means to be tardy, and there is often a connection of a similar root with heaven, which could be because the heaven stands still at the axis about which everything revolves.
kesha, said to be from klish, to torment, is the hair on one's head or the mane of an animal, and keshava is one with long hair, or one with a mane. It is an epithet applied to Krishna about whom I wrote in connection with Brijesh, see
http://www.behindthename.com/bb/arcview.php?id=207404&board=gen and my own followup to that. Brajesh is more pastoral term than keshava, but keshava still refers to this particular incarnation of viSNu, and used in a much more `human' context than the general name for the protector all-pervading viSNu (worker).