For most of my life 'till about a couple of years ago, I had only seen the spelling orangutan written to describe those delightful red-headed apes from the tropical forests of Borneo. Lately, though, I've increasingly been seeing a strange spelling in certain scientific publications I read: orang-utan, with a hyphen. Is there a particular reason why this hyphen was added? It's strange, because usually in English, words evolve to have their hyphens and diacriticals omitted, not added.
Perhaps this phenomenon should have a name, maybe "hyphen decay". A noun phrase becomes so current that starts being treated as a single word and is granted a hyphen in recognition of its new status. If the word becomes popular enough, even the hyphen is dropped and the words fuse.
"Bell boy" becomes "bell-boy", then "bellboy". Ditto for hundreds of other words from "type writer" to "lap top".
Orangutan is unusual in that the words originated in a non-Western language (albeit one that used Latin characters) and the hyphen was apparently added in the process of importing the word into English.
The correct way when I was growing up in Singapore is that it's an orang utan (two words) because 'orang' means Man in Malay (one of our national languages) and 'utan' means Forest. So literally - Man of the Forest. The pronunciation is oh-rung u-tahn, not oh-rang-a-tan which remains really strange to hear. The hyphenation probably came about when someone wanted to correct it without wanting to separate the two words.