in English is:

helpful

,

useful

Mutations

Soft:ddefnyddiol
Nasal:nefnyddiol
Aspirate:(no mutation)
External

Dictionary Portal

This is a library of dictionaries and other online resources where you can search further for defnyddiol*:

Specialist Dictionaries
Glossaries
Terminology
Encyclopedia
Example Sentences
Sentences containing:

*External websites will be opened in a new window.