Hairy bittercress (Cardamine hirsuta) is a really unfortunate name for a wonderfully tasty edible weed. Bittercress is a mustard, so its bitterness is more spicy-hot than bitter, though it’s not nearly as hot as some other members of the Brassicaceae family.
The “hairy” in its name is derived from the tiny “hairs” on its leaves and stems. The hairs are more noticeable on young bittercress, but you still have to look pretty hard, like with a loupe or magnifying glass, to see them. A more appropriate name would be Not-so-hairy and pleasantly-mild spicycress.