The term 'prickly seedcase' refers to a BURR, which is a small, dry fruit with hooks or prickles that attach to fur or clothing. The two crossword solutions for this term are BURR (4 letters) and BUR (3 letters). A BURR is a type of fruit that has a hard outer shell and contains one or more seeds. It is often found on plants such as thistles, burdock, and teasel. The burrs can be difficult to remove from clothing or fur due to their sharp spines.