WordWeb Online

1. So lacking in interest as to cause mental weariness
   "a ho-hum speaker who couldn't capture their attention";
   - boring, deadening, dull, irksome, slow, tedious, tiresome, wearisome, unamusing, deadly [informal], draggy [informal], mind-numbing

See also: lame, lameo [informal], meh [informal], samey [Brit, informal], uninspiring, uninteresting

Encyclopedia: Ho-hum