Many items in the spice aisle of the grocery store are a single spice or herb, dried, chopped or ground, etc. Curry powder, however, is not a single spice or herb. When purchasing curry powder, different brands will have different amounts of the spices, and sometimes other spices added.
Most curry powders usually include coriander, turmeric, cumin, and fenugreek in their blends. Additional ingredients such as ginger, garlic, fennel seed, cinnamon, clove, mustard seed, green cardamom, black cardamom, mace, nutmeg, red pepper, long pepper and black pepper may also be added.
The curry powder I have on hand contains coriander, fenugreek, turmeric, cumin, black pepper, bay leaves, celery seed, nutmeg, cloves, onion, red pepper, and ginger.
GF - because curry powder is not a single spice, there is a slight possibility of gluten in some brands. The McCormick company is very dependable on this subject and does not hide wheat on their labels (if it's there, it'll say "wheat", not "natural flavours"). At the time of this writing, McCormick curry powder is gluten-free, as are most others.