Definition of weaksauce:
(adj) :
(originally and chiefly US, informal) Lacking in interest or substance; boring, disappointing, lackluster.
(n) :
(countable) Someone or something that is lacking in interest or substance.
(n) :
(uncountable) The quality or state of lacking in interest or substance; boringness, disappointment.
(n) :
(uncountable) Synonym of weak tea (“weak or feeble arguments, efforts, or proposals”).