Webster's Revised Unabridged Dictionary · 1913

Mawkishly or weakly good; exhibiting goodness with silliness. [Colloquial]

A person who is weakly, sentimentally, or affectedly good; a goody-goody person; -- sometimes used to refer to person who acts with good intentions but who bunglingly does more harm than good. The latter may sometimes be deprecatingly referred to as a goo-goo. [Colloquial]