A fragrance was a chemical compound that had a distinctive odor or flavor. A perfume was a type of fragrance.
Retaya was a Flaxian assassin who operated as a merchant who dealt in fine wares, mostly fabrics and fragrances.
Because Odo did not have a sense of smell, he had Retaya guide him through the scents in his sample case, during his attempt to find a "gift for a friend" – a "lady friend" – by describing the fragrances for him. Of the three samples Odo selected, the first sample had "a somewhat floral bouquet"; the second was "more musky than the first"; and the third was described as "spicy".
When Odo began choosing his selections, he decided that "I think she would like something both floral and musky," before suggesting that he mix the first two. Retaya agreed, and found the combination to be "very nice." Odo continued, "But on the other hand, she's also quite fond of spicy things," before suggesting that he add a drop of the third fragrance. Retaya, this time, stopped Odo, and explained that "I really don't think they would go well together," and when Odo urged on, Retaya continued, "I really don't think your lady friend will like the aroma." Odo finally revealed that, in fact, "when these three fragrances are combined, they produce a gaseous mixture that can trigger a fatal heart attack when inhaled." Retaya feigned ignorance, repeating that "I simply didn't think your friend would like the aroma," before asking to be allowed to leave. (DS9: "Improbable Cause")