The adjective roterodamus means “of Rotterdam” (the city in Holland). To lovers of Latin, unless they entertain an unusual interest in Dutch geography, the word is familiar probably primarily because of Erasmus of Rotterdam (Erasmus Roterodamus). But how is it pronounced?
I would expect all vowels to be short. The stress would then fall on the antepenultimate syllable, i.e., roteROdamus. In this video, Terence Tunberg, an expert Latin writer whose authority I have no business questioning, certainly stresses it on that syllable. It also sounds quite a bit like he pronounces it with a long o, i.e., roterōdamus.
It is strange, though, that a vowel that does not even occur in the original name of the town should be stressed that way. (The name is in fact stressed on the last syllable in Dutch.)
I have a collection (1) of selected Colloquia by Vives, Cordier and Mosellanus, annotated for use in Latin education, which contains Mosellanus' Dialogus IX, where it says:
[…] hymnos Aurelii Prudentii, gravis et sancti viri, audiemus aut, si hi displiceant, 'Enchiridon militis Christiani' ab Erasmo Roterodámo accuratissime elaboratum.
I take the accent over the a to indicate a non-standard stress on the penultimate syllable (whether all vowels are short or not, we would not expect it there). It was placed there by the editors, the original did not have it. But it makes sense to me.
Which pronunciation is correct?
(1) Lore Wirth-Poelchau, Wolfgang Flurl (ed.): Lateinische Schülergespräche der Humanisten, Bamberg 1992.