a (usually) large and scholarly book
"The dusty library shelf was filled with heavy tomes on medieval history that few people ever read."
One in a series of volumes.
"The librarian carefully shelved the second tome of the ancient encyclopedia after binding it."
In plain English: A tome is a very large and heavy book that usually contains a lot of detailed information.
"The old library was filled with dusty tomes that no one ever reads anymore."
A surname.
"Tom Tome is a well-known historian who specializes in ancient texts."
The word "tome" comes from the Middle French tome, which was borrowed from Latin and originally referred to a section or roll of papyrus. Its ultimate origin is Ancient Greek, where it meant both a volume and something that had been cut off.