Let's crack out the Shorter Oxford:
Aasimar/aasimon: Nothing. Closest term: aasvogel (from old Afrikaans aas carrion + vogel bird) A vulture.
Odd.
Genasi: Nothing. Closest term: gena, from Latin for cheek. In an invertebrate, especially an insect, either lateral part of the head below the level of the eyes.
Odder.
Sahuagin: Nothing. Closest term: Sahuaro, variant of Saguaro, probably from Uto-Aztecan: A tree-sized branching cactus, found in desert regions of Mexico and the south-western USA.
That's just worryingly odd.
Tiefling (and by the way, for those who don't speak German, 'ie' is pronounced 'ee' not 'i' in that language): Nothing. But the closest term is indeed Tief, pronounced 'teef', a West Indies word, both verb and noun, meaning 'to steal' or 'thief'.
That's actually fairly appropriate...