Final answer:
The blank can be filled with the vocabulary word 'impasse'. An impasse refers to a situation in which progress is blocked or halted due to a disagreement or deadlock between two or more parties.
Step-by-step explanation:
The blank in the sentence can be filled with the vocabulary word impasse. An impasse refers to a situation in which progress is blocked or halted due to a disagreement or deadlock between two or more parties. In this case, the two groups wanting to meet on different days caused an impasse, resulting in the cancellation of the outing.
Learn more about Vocabulary word 'impasse' for disagreement or deadlock