Kala jeera or kalonji seeds are often confused with black sesame seeds because of their similar appearance, but one whiff will set even a layman straight.
Onion seeds or nigella seeds are often used to flavour bread products in the west, while in india, particularly in Bengal, it is popular both as a standalone spice and also as a part of paanch phoron.
This is as compatible with vegetarian dishes as with fish preparations. Temper the blandest vegetable with a combination of onion seeds and garlic, and marvel at the difference.