Shiva Purana
रुद्दुःखं दुःखहेतुर्वा तद्रावयति नः प्रभुः ॥ रुद्र इत्युच्यते सद्भिः शिवः परमकारणम् ॥ ३६ ॥
The explanation of the word Rudra:—‘Rud’ means misery and ‘Drāvayati’ means ‘routs’. Since the lord quells our misery he is called Rudra. He is Śiva, the great cause.
english translation
rudduHkhaM duHkhaheturvA tadrAvayati naH prabhuH ॥ rudra ityucyate sadbhiH zivaH paramakAraNam ॥ 36 ॥
hk transliteration by Sanscript