a mortise joint formed by interlocking tenons and mortises
source: WordNet 3.0
A flaring tenon, or tongue (shaped like a bird's tail spread), and a mortise, or socket, into which it fits tightly, making an interlocking joint between two pieces which resists pulling a part in all directions except one.
source: Webster 1913
fit together tightly, as if by means of a dovetail