Fenugreek seeds
Small, hard, yellowish-brown seeds with a bitter aroma, faintly reminiscent of maple syrup, that develops when toasted in fat.
Fenugreek seeds are sold in Turkish or Indian grocers, Asian shops, spice merchants and often health food stores, less often on the spice shelf of an ordinary supermarket. They are briefly fried in hot oil or ghee until they darken and become fragrant. Taken too far, they turn harshly bitter.
Substitute:
There is no true substitute. Dried fenugreek leaves come close to the aroma but lack the bitterness and bite of the seeds. Mustard seeds crackle similarly in oil but taste different. When in doubt, it is better to leave the seeds out than to substitute poorly.