The word that has a different vowel sound among the options provided is "palm." Here's why:
1. **Van:** The vowel sound in "van" is /æ/ as in the word "cat."
2. **Trap:** The vowel sound in "trap" is /æ/ as in the word "cat."
3. **Jam:** The vowel sound in "jam" is /æ/ as in the word "cat."
4. **Palm:** The vowel sound in "palm" is /ɑː/ as in the word "car."
In this case, "palm" is the word that stands out as having a different vowel sound compared to the other words provided (van, trap, jam).