Green’s Dictionary of Slang

babu n.

also baboo
[Hind. babu, a term of respect (Mr, Esquire) or an educated man]
[20C+] (W.I.)

1. (also baboo-boy) an old East Indian man, usu. bearded and poor.

2. (also babu-man) an ugly old man.

3. (also babu-man) an imaginary figure, ugly and old, conjured up to frighten children.