/ ˈgɑːgɑː; NAmE / adjective [ not usually before noun ] ( informal )
1.
( offensive ) confused and not able to think clearly, especially because you are old :
He has gone completely gaga.
2.
slightly crazy because you are very excited about sb/sth, or very much in love :
The fans went totally gaga over the band.
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WORD ORIGIN
early 20th cent.: from French , senile, a senile person , reduplication based on gâteux , variant of gâteur , hospital slang in the sense bed-wetter.