I was invited to dinner（at their house， in the ordinary way）．
I was invited to a dinner given to welcome the new ambassador．
You can memorize words in an efficient way if you pronounce them reasonably. Say words correctly, and you will learn them easily. Correct pronunciation means correct spelling of the words. English spelling is not good to guide its pronunciation. But spelling and pronunciation have closed relationship. They match each other perfectly. Sometimes we can pronounce a word according to its spelling. English pronunciation can also guide its spelling. This is a two-way communication.