Should I hyphenate a word that begins with the prefix mega? Should I write megacity or mega-city?
Interestingly, there has been a shift or progression in the spelling of megacity. Both the 2004 Canadian Oxford Dictionary and the 2003 Gage Canadian Dictionary spell it as one word: megacity. However, the 1998 edition of the Oxford lists the hyphenated spelling mega-city.
There appears to be a natural evolution for compound words in English. It is quite common for them to begin as two words (e.g. on line), to become hyphenated (e.g. on-line), and to end as one word (e.g. online).
Although it appears that megacity has followed this pattern, many would not consider it a mistake to write mega-city.