Coconuts are part of the Aracaceae family of plants so are more similar to palm plants, banana and pineapple than they are to tree nuts. There is little evidence that coconut should be avoided if you suffer from a nut allergy.
Coc n 1 is a major allergen associated with allergy to coconut - it is classified as an inhalent allergen rather than an ingested food allergen.
There is some evidence that coconut can cause contact dermatitis rashes - this is due to cocamide diethanolamine (Cocamide DEA). These are fatty acids found in coconut which are used in many cosmetic products. If sensitised to cocamide DEA you will still be able to eat the fruit from a coconut without any reactions.
There are no syndromes associated with coconut allergy.
There is limited evidence of cross reactivity with walnuts and lentils.
Systemic allergic reaction to coconut (Cocos nucifera) in 2 subjects with hypersensitivity to tree nut and demonstration of cross-reactivity to legumin-like seed storage proteins: new coconut and walnut food allergens, 1999