pentomino
/pɛnˈtɒmɪnəʊ/noun
1Each of the twelve distinct planar shapes that can be formed by joining five identical squares by their edges.
2In plural A board game or puzzle involving the rearrangement of plastic or wooden pentomino shapes.
Origin
1950s; earliest use found in American Mathematical Monthly. From penta- + -omino; coined by S. W. Golomb by analogy, taking the d- of domino (by an intentional false etymology) to represent either di- or duo-.