Which word means strange or funny because a situation is different from what is expected?

The term "ironic" is used to describe a situation where there is a notable difference between what is expected and what actually occurs, often leading to humor or a sense of strangeness. This word captures the essence of unexpected outcomes that can be both amusing and thought-provoking. For example, if someone plans a picnic on a sunny day and it unexpectedly rains, the irony lies in the contrast between their intention and the outcome.

In contrast, "significant" refers to something important or meaningful, without the connotation of surprise or humor. "Tense" describes a state of mental or emotional strain, which does not relate to the notion of expectation. Meanwhile, "compelling" typically means something that draws attention or is convincing; while it may be interesting, it does not convey the specific sense of unexpectedness and humor that "ironic" does. Therefore, "ironic" is the most accurate choice for the definition given in the question.