the physical part of language, i.e. the letter

letter:

visual / symbol / glyph

sign or part of sign

system component

variable unfixed

flighty unstable volatile

loaded free and not free

before mess or message

upper limit something not quite speech

lower limit more or less than phoneme

not the letter of the law

but the interpretation of the law of the letter

frame bumps arrows cups fork tines trees

crosses holes with lines differential strokes

curves and intersections