NATIONAL NUT DAY

October 22 is NATIONAL NUT DAY.  Gerald, Les, and I love nuts with cashews being the favorite. My grandfather had butternut trees and I have not tasted them in years but I recall that they are delicious.

I am not interested in inedible nuts such as acorns and buckeyes and some edible seeds and dry fruits are sometimes confused with nuts.  Peanuts are legumes, not nuts.  After researching, I compiled this list of true, edible nuts:

ALMONDS
BEECHNUT
BUTTERNUT
BRAZIL NUT
CANDLE NUT
CASHEW
CHESTNUT (includes CHINESE, MALABAR, PORTUGUESE, and SPANISH CHESTNUTS)
HAZELNUT (FILBERTS and COBNUTS are the same as HAZELNUTS)
HICKORY NUT
PECAN
PINE NUT
KOLA NUT
MACADAMIA
OGBONO
PILI NUT
PISTACHIO
WALNUT

I have eaten all of these except for CANDLE NUTS and OGBONO, but will search to find some.  I only know about BEECH NUT because of BEECH NUT gum. I  knew PILI NUTS because I worked with a woman from the Phillipines who spoiled me with traditional cooking from her homeland.

My question:  WHY are some nuts ONE word while others are TWO words (BUTTERNUT versus HICKORY NUT, for example)?