Asm: ডিব্ৰুগড় ḍibrugaṛa
‘Fort on the River Dibru’ [Dibrumukh] City/District, Assam
From Bod: dibru, ‘River Dibru’ [Bod: di, ‘water’, ‘river’; and dib(a)ru, ‘blister’] and Asm/Hin: mukh, ‘mouth’; garh, ‘fort’, ‘rampart’.
The mukh in Dibrumukh, ‘mouth of the river Dibru’ is still used but Dibrugrah is generally preferred. It’s not clear how ‘blister’ fits into the derivation of the river’s name, but it is widely cited in reputable sources e.g. Phukan (2001).
The Dibru river starts in the low hills, joins the Doomdooma river, creating wetlands at Maguri Beel near Tinsukia and finally flows into the Brahmaputra near Dibrugarh.
Dibrugarh’s real claim to fame is that its railway station is the starting point for the longest railway journey in India: the 15905/15906 weekly Dibrugarh – Kanyakumari Vivek Express travels 4,234 km to the southernmost point in India, the journey takes 79 hours.