Are you talking about the icon that's to the left of the trash can icon (it sort of matches the description you give but, I know, it's notorously difficult to describe icons!). If so, this is the 'move email' icon. It enables you to move an email from one folder to another (even from one email account to another).
If you touched it accidentally and then did some 'other stuff' after that, it's probably only moved the email you're after to another folder. Have a look through your folders (I hope you don't have too many!) and you should locate it.
Then you can use the 'move' icon again to restore the email in question to its 'rightful place'!
If I've misunderstood the icon you're referring to, please forgive me and let us know and we'll try and help.
Good Luck and enjoy your iPad.
Tim
Scotland