aneurysm

From Ancient Greek ἀνεύρυσμα (aneúrusma), 'a widening, a dilation,' from the verb ἀνευρύνω (aneurúnō), 'to dilate,' itself built from ἀνά (aná, 'up') plus εὐρύς (eurús, 'wide').

The word stayed close to its roots: it named a widening or dilation in Greek, and it names a widening — of a blood vessel — in English today.

Its root eurús, 'wide,' is the same idea baked into the Greek verb aneurúnō, 'to dilate up' or 'widen out,' from which the noun form was built directly.