The correct answer is thanks was.

Explanation:
In standard English grammar, the noun phrase "vote of thanks" refers to a single formal proposal or expression of gratitude offered at a meeting. Here, the subject of the sentence is the singular noun "vote" (modified by the prepositional phrase "of thanks").

Since the subject ("vote") is singular and the action took place at a specific time in the past (at the end of the meeting), it requires a singular past tense verb, "was".
Therefore, the complete correct phrase is "thanks was" (completing "A vote of thanks was proposed at the end of the meeting").