皮肉

彼の褒め言葉には、どこか ___ を含んだ響きがあり、素直に喜べなかった。

The correct answer is **皮肉 (ひにく)**, meaning irony or sarcasm. The sentence states, "His compliments contained a certain ____, so I couldn't honestly be happy." If the compliments had an underlying layer of sarcasm, it would naturally make one unable to genuinely feel pleased. **賛美 (さんび)** and **称賛 (しょうさん)** both mean praise or admiration; if the compliments contained these positive elements, one would typically be happy, contradicting the sentence's latter half. **尊敬 (そんけい)** means respect, which is also a positive sentiment, making it unsuitable for the context of inability to rejoice. The key is the negative emotional outcome.

正解は「皮肉」です。褒め言葉の裏に「皮肉」があれば、素直に喜べないのは当然です。「賛美」や「称賛」は褒める意味、「尊敬」は敬う意味で、いずれもポジティブな感情なので、「素直に喜べなかった」という文脈とは合いません。文末の感情がヒントです。