(More or less)

四角四面
shi.kaku.shi.men

Literally: four – corner – four – face

Alternately: Square. Four (equal) angles and four (equal) sides, just like it says. By extension, a “square” personality: extremely, perhaps even overly, serious. Meticulous; stiff; formal; lacking a proper amount of flexibility and vagueness.

Notes: This really does seem to be setting up a certain “vagueness” as a virtue; several of my sources cite a surfeit of はっきり (“clearly,” “distinctly,” definitively”) as one of the problems of squareness.

What could be more serious and formal than a squared square?