I often encounter the word superlative in my English language teaching, but it also cropped up recently in a business magazine article I was subediting. When I first encountered superlative, I reasoned that it was pronounced super-lative, just as superfluous was super-fluous. But they’re not: they are su-per-luh-tive and su-per-flu-ous respectively.
Even though super comes from Latin, most English words starting with that morpheme are modern, and are attached to real English words, whether nouns, verbs, adjectives or adverbs. Super retains its usual stress and so does the real English word following it. Lative and fluous aren’t English words, but many others based on Latin ferre/fero/latus and fluere/fluo/fluxus are. Note also that superlativus and superfluus were/are real Latin words. Wikitionary says that the pronunciation of superfluus was as in English, but that of superlativus was super-lativus. (By the way, the literal meanings in Latin and English are ‘carried over’ and ‘flowing over’.)
There are three other English words which are pronounced su-per rather than super: superb, superior and the rare supernal. –b, –ior and –nal are clearly not English words, and in fact represent the Latin suffixes –bus, –ior, and –nalis – the Latin words were superbus (not super-bus), superior and supernalis (not sure of pronunciation).
To sum up: don’t embarrass yourself in public by pronouncing these two words as super-lative and super-fluous.
Never Pure and Rarely Simple 