I’ve just learned the Japanese word for twins which is 双子 (ふたご), however my dictionary says that it can also be read as そうし. Interestingly enough WK doesn’t mention that reading, is that because it is rare or outdated?
Checked with a native speaker who said そうし is not a common reading. She wasn’t familiar with it at all. That being said, there are some readings that WK is lacking that are actually common. You win some you lose some.