A person unusually devoted to reading and study. (Merriam – Webster)
A person who reads a lot. (Cambridge Dictionary)
A person who enjoys reading. (Oxford Dictionaries)
(especially formerly) the larva of a wood-boring beetle which feeds on the paper and glue in books. (Oxford Dictionaries)
A person devoted to reading or studying. (Dictionary.com)
Any of various insects that feed on books, especially a booklouse. (Dictionary.com)
If you describe someone as a bookworm, you mean they are very fond of reading. (Collins Dictionary)
Seven must known animal idioms.
Novel news: world’s biggest bookworms revealed in study.