
1) Backed 2) Book format 3) First printing, often 4) Hardback 5) Hardbacked 6) Hardbound
Found on
https://www.crosswordclues.com/clue/hardcover

1) Backed 2) Hardback 3) Hardbacked 4) Hardbound 5) Shell
Found on
https://www.crosswordclues.com/clue/hardcover

A hardcover, hardback, or hardbound book is one bound with rigid protective covers (typically of cardboard covered with cloth, heavy paper, buckram, or occasionally leather). It may have a flexible, sewn spine which allows the book to lie flat on a surface when opened, or have a glued spine. Following the ISBN sequence numbers, books of this type ...
Found on
http://en.wikipedia.org/wiki/Hardcover

Book bound with hard cardboard cover, then covered with a paper dust jacket.
Found on
http://www.word-mart.com/html/glossary1.html

A book bound with a thick cardboard stock cover, usually with a paper dust jacket.
Found on
https://thgmwriters.com/blog/glossary-writing-definitions/
No exact match found.