Head case and Wing nut

Head case noun - A person judged to be legally or medically insane.

Wing nut and head case are semantically related. In some cases you can use "Wing nut" instead a noun phrase "Head case".

Wing nut noun - Any tree of the genus Pterocarya; fruit is a small winged nutlet; Caucasus to southeastern Asia.

Head case and wing nut are semantically related. Sometimes you can replace phrase "Head case" with "Wing nut", this phrases are similar.