Answer:
Semiquaver, though this is not what it means in reality.
Step-by-step explanation:
Dichotomy - wrong because di- means 2, not half (it's a problem w/ 2 choices)
Semiquaver - I think right? semi- means half, though the ACTUAL meaning is half of an eighth note, or just a regular 16th note
Antediluvian - wrong because it refers to the biblical time before (ante-) the flood (-diluvian), nothing to do with music
Biennial - wrong because bi- here means two, and -ennial means yearly. The word itself means once every two years
Semiquaver is the only one that's close. I hope this helps!