The term 'taciturn' describes an individual who is typically quiet and disinclined to speak. Identifying the correct antonym requires a word signifying the opposite characteristic: being talkative.
Let's evaluate the provided choices:
- reserved: This term aligns with 'taciturn', indicating a disposition towards quietness and restraint.
- vehement: This word denotes intense emotion or conviction and has no connection to speaking habits.
- garrulous: This adjective signifies excessive talkativeness, particularly concerning trivialities, thus presenting the direct opposite of 'taciturn'.
- ungraceful: This descriptor pertains to a lack of elegance or poise, irrelevant to vocal behavior.
Consequently, the appropriate antonym for 'taciturn' is garrulous.