the compound adjective 'straight-sided' is a modern english formation built from native germanic elements. its first element, 'straight', originates from the old english concept of being stretched taut, which evolved to denote a line free from curves or bends. the second element, 'side', has maintained a remarkably stable meaning from its old english root referring to the flank or lateral boundary of an object. the adjectival suffix '-ed' is appended to the noun 'side', a common pattern in english for creating descriptive terms like 'blue-eyed' or 'long-haired'. thus, the word's literal construction, 'having sides that are straight', directly and transparently conveys its precise geometric meaning, showcasing english's capacity for logical compound formation.

Structure: straight (not curved) + side (lateral surface) + ed (having the quality of) straight (from middle english 'streght', meaning direct or not curved; old english 'streht', past participle of 'streccan' meaning to stretch; functional role: adjective base describing form). side (from old english 'sīde', meaning the flank or lateral part of something; functional role: noun base specifying location). ed (from old english '-ed', '-od', '-ad', a suffix forming adjectives from nouns, meaning 'having' or 'provided with'; functional role: adjectival suffix).