Can you think of five four-letter words, each beginning with SE?
Sounds simple, however you cannot use a letter more than once, and you can’t re-use the S or the E anywhere else. So for instance, SELL is not allowed, as it has two Ls, SEEK is not allowed as it repeats the E, and you cannot have both SENT and SEAT, as both have a T, but either word is acceptable on its own.
