Source : Webster's Revised Unabridged Dictionary (1913)

Burdensome \Bur"den*some\, a.
   Grievous to be borne; causing uneasiness or fatigue;
   oppressive.

         The debt immense of endless gratitude So burdensome.
                                                  --Milton.

   Syn: Heavy; weighty; cumbersome; onerous; grievous;
        oppressive; troublesome. -- {Bur"den*some*ly}, adv. --
        {Bur"den*some*ness}, n.

Source : WordNet®

burdensomeness
     n : unwelcome burdensome difficulty [syn: {onerousness}, {oppressiveness}]