noun
tenon
TEN-un/ˈtenən/
A projecting end of a piece of wood shaped to fit into a matching socket.
The wooden tenon projects from the rail toward its matching socket.

Etymology
Tenir means “to hold”: a tenon is the projecting piece inserted into a matching opening to make a joint. Its name connects the projection with its holding function.
In context
the piece that has the tenon in it and that's the square peg at the end that fits into a mating square hole
More examples
- Each rail has a tenon that fits into the chair leg.
- She trims the tenon until it slides snugly into the mortise.
- Glue holds the two tenons securely inside their sockets.
Forms
tenon · tenons
Similar words
- projection
- Any protruding part, not necessarily shaped to fit a socket.