The term "blood knot" refers to a type of fishing knot that is commonly used to join two pieces of fishing line together. However, there are several synonyms for this term that can be used interchangeably in different contexts. One synonym is the "barrel knot", which is similar to the blood knot but is slightly easier to tie. Another synonym is the "double fisherman's knot", which is a more complicated knot that is commonly used by climbers to join two ropes together. Other common synonyms for the blood knot include the "water knot" and the "granny knot", both of which are used in different types of knotting applications.