opprobrious (adj.) [...] from Latin opprobare "to reproach, taunt,"
from ob "against" (see ob-) + probrum "reproach, infamy." Etymological sense is "disgrace attached to conduct considered shameful." Related: Opprobriously; opprobriousness.
When I first encountered this word, I interpreted ob as a negation/negatory prefix, in opposition to probum. This interpretation is wrong, because it would mean that oppobare meant the opposite of its true meaning.
Prefixes still bedevil and beset me; so please disambiguate the meaning?
Etymonline's separate entry on ob-, states one use 'as an intensive'. However, this use seems unlikely here, because then Etymonline would've have written thus in the entry above.