Why OAK is not called "acorn tree" and acorn is not an "oaknut", they sound so different?

Answer 1

Great question! But probably one that belongs in the languages section.

For some reason the seed of the oak tree is called an oak corn (OAKCORN-ACORN), rather than an oak seed or nut. In history the pronunciation of the word oak would have been more like an 'A' sound. German and English have a common root and in German the oak is called Eich. In German one would say oak-corn as Eich-korn (although the German word for an acorn is actually Eichel).

I guess it was just a very old word that stuck well and resisted change. Maybe in Olde English a hazel nut was called a hazel corn? Just guessing.

UPDATE: This website says that acorn in fact comes from an Olde English word 'aecern', meaning a fruit or berry:
http://www.phrases.org.uk/bulletin_board/42/messages/1082.html

FURTHER: This website says that acorn comes from an Old Norse word 'Akran', which means the fruit of any wild tree:
http://starling.rinet.ru/cgi-bin/etymology.cgi?single=1&basename=/data/ie/germet&text_number=+++554&root=config