Just as the three usual spatial dimensions have terms to refer to their measurement -- height, width, and depth -- so does the fourth spatial dimension. Spissitude is currently the most common term used to refer to measurement of an object's extension along the fourth dimensional axis (i.e., the w axis). Just as height has two directions, up and down, spissitude has two directions, ana and kata.
While the terms ana and kata are generally recognized, spissitude is less commonly used. This is in part because it is somewhat uncommon to refer informally to size in the fourth dimension, but also because it has an unfortunate etymology. Spissitude was originally used to refer to the fourth dimension by Henry More, who considered the fourth dimension to be the realm of the spirit. Spissitude, in his mind, referred to the depth or 'denseness' of the spirit, mirroring the original meaning of the word, i.e., dense, compact, or thickened.
Scientists and mathematicians, being of a more material and evidence-based mindset, found this association unpleasant. However, the only other term that has gained any real traction, 'trength', remains a distant second in "common" usage. It is worth noting that trength and the associated terminology introduced by Garrett Jones is fairly well developed, including terms for "short in the forth dimension" ('tarrow') and "long in the fourth dimension" ('trong'), among various others.