I've seen that the Australian's use the term 'pronumeral' to describe 'letters that stand for a number'. Do we have an equivalent term or phrase? I particularly dislike using the term 'variable' because, in an equation, 'x' often has a constant/fixed value and so calling it a variable seems certain to promote deep conceptual mis-understandings and confusion. 'Parameter' doesn't fit well either. When finding a missing angle 'a' in a triangle, say, it doesn't seem appropriate to call it a parameter, and certainly not a variable. 'Attribute' is quite close (as used in some programming languages)? I would like to be mathematically accurate, without promoting mis-understandings. My only concern with 'pronumeral' is that it doesn't seem (at all) in common usage in the UK.