dot ‧ ty /ˈdɒti $ ˈdɑːti/ BrE AmE adjective old-fashioned informal
[ Date: 1800-1900 ; Language: Scottish English ; Origin: dottle 'stupid person' , from dote 'to be stupid' (12-19 centuries) ]
1 . slightly crazy
2 . dotty about somebody/something liking or loving someone or something very much:
Gemma’s dotty about horses.