idiom.
(out to lunch) Not in touch with the real world; crazy.
The Century Dictionary and Cyclopedia
noun.
A large lump or piece, as of bread.
noun.
A slight repast or meal between breakfast and dinner, or, as formerly, between dinner and supper, or between dinner or supper and bedtime; luncheon.
To take a lunch or luncheon.
the GNU version of the Collaborative International Dictionary of English
noun.
A luncheon; specifically, a light repast between breakfast and dinner, most commonly about noontime.