Sentence:  When John bites down on Sherlock's neck as his <WSD>knot</WSD> locks them together, the act which would otherwise be a tool for domination only reinforces the existing emotional bonds they have for each other. 
Meaning of the word marked with <WSD> tags:  In omegaverse fan fiction, a bulbus glandis-like structure on the penis of a male alpha, which ties him to an omega during intercourse.