One of the mysteries of the English language finally explained.
Building, Engineering, and Nautical. Any of several kinds of device for holding something in place or holding two things together.
Late Middle English (in an earlier sense). Apparently from dog + bolt, although this may not be the case in senses A. 1 and A. 2. In spite of the chronology, it is possible that sense A. 2 was the earliest meaning, and that the word is from dog + bolt, in which case dog perhaps carries the connotation ‘of little value’, perhaps in this context specifically ‘such as might be shot at a dog’; sense A. 1 may (in spite of the chronology) show an extended use of this.
dog bolt/ˈdɒɡ bəʊlt/
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