obversal
It's like flipping a coin, but instead of heads or tails, it's front or back, and sometimes it's just a coin or a flag.
He flipped a coin and called it the obverse. No one asked what the reverse was.
She looked at a flag and said the obverse was on top. No one cared.
He flipped a coin, called it a flag, and said it had two sides. Everyone was confused.