The term 'Tetra-Doubled' refers to a combination of two words, 'tetra' and 'octo'. Tetra is a prefix meaning four, while octo is a prefix meaning eight. Therefore, the term 'Tetra-Doubled' refers to a combination of four and eight, or twelve. This combination can be seen in the crossword solutions OCTA (4 letters) and OCTO (4 letters). Together, these two words form the term 'Tetra-Doubled', which is a combination of four and eight, or twelve.