The affix ṭhak comes after a word in the Accusative -2nd case in construction when the sense is 'who makes a sound or croaking'.,
Thus शब्दं करोति = शाब्दिकः 'who makes a sound' i. e. a Grammarian. So दार्दुरिकः 'who makes a croaking noise like a frog (dardura)' i. e, a potter.,