The term 'prickly seed husk' refers to the hard outer covering of a seed, which is often covered in spikes or thorns. The crossword solution for this term is 'BUR, ' which is a type of seed dispersal that occurs when an animal eats the seed and then excretes it elsewhere. This method of seed dispersal is common in many plants, including cacti, and helps to spread the plant's seeds over a wide area.