From WordNet (r) 3.0 (2006):
burden
n 1: an onerous or difficult concern; "the burden of
responsibility"; "that's a load off my mind" [syn:
burden, load, encumbrance, incumbrance, onus]
2: weight to be borne or conveyed [syn: load, loading,
burden]
3: the central meaning or theme of a speech or literary work
[syn: effect, essence, burden, core, gist]
4: the central idea that is expanded in a document or discourse
v 1: weight down with a load [syn: burden, burthen,
weight, weight down] [ant: disburden, unburden]
2: impose a task upon, assign a responsibility to; "He charged
her with cleaning up all the files over the weekend" [syn:
charge, saddle, burden]