"Ο θείος θα έχει βρει το περιοδικό."

Translation: The uncle will have found the magazine.

[jaye16]

Oddly enough periodical is an adjective and a noun. It is something published at regular intervals. So, it is a kind of magazine.

[JimAthanas1]

'periodical' should also be accepted

[jaye16]

Yes, thank you. I've added it.