specialized dictionary
A dictionary covering a specific field, such as law, medicine, or computing, rather than a general-purpose dictionary.
I bought a specialized dictionary of medicine.
This specialized dictionary explains legal terms in detail.
辞書 is a general dictionary; 専門辞書 is a specialized dictionary for a particular field.
事典 is an encyclopedia covering broad knowledge; 専門辞書 focuses on terminology within a specific domain.
Compound of 専門 (せんもん, 'specialty') and 辞書 (じしょ, 'dictionary').