Source : Webster's Revised Unabridged Dictionary (1913)

Misspend \Mis*spend"\, v. t. [imp. & p. p. {Misspent}; p. pr. &
   vb. n. {Misspending}.]
   To spend amiss or for wrong purposes; to aquander; to waste;
   as, to misspend time or money. --J. Philips.

Misspent \Mis*spent"\,
   imp. & p. p. of {Misspend}.

Source : WordNet®

misspend
     v 1: spend time badly or unwisely; "He misspent his youth"
     2: spend (money or other resources) unwisely
     [also: {misspent}]

misspent
     See {misspend}