Fennel seeds
Fennel seeds, another member of the parsley family, are a tasty substitute for cumin. Fennel seeds, as opposed to cumin, have an anise-like, licorice taste. When you're in a bind, they won't taste out of place but won't have the same smokiness and earthiness as cumin. Use fennel seeds in place of cumin seeds and crushed fennel in place of cumin seeds. Remember that you can always crush fennel seeds in a food processor or coffee grinder for a little period of time.
Start out cautiously, using around half the quantity of cumin called for in the recipe, just like with the other spice substitutes. After that, add the spice a pinch at a time, tasting as you go. Consider using a sprinkle of coriander in your meal as well if you miss the smokey taste.