I can't get started this morning! The word is M?M??? but the letter after both Ms is the same. The only word I can come up with is MIMICS but it means the word going down would be S?IC ...it's got me stumped!
Ooh good thinking Baldrick! Never thought of that one. There are no clues Sandy it's just one of those where you get a letter or two to start you off and have to fit words round it.