The word "spineless" is a transparent compound formed within English from the noun "spine" and the adjectival suffix "-less." The noun "spine" itself has a long history, tracing back to Latin spina, meaning "thorn" or "backbone," which is thought to derive from the Proto-Indo-European root spei-, meaning "sharp point." The literal biological sense, "having no spinal column," emerged first, applying to invertebrates. The figurative meaning, describing a person lacking moral fortitude or resolve, developed through a powerful metaphor: just as a physical spine provides structural support to a body, a figurative "spine" provides courage and determination to a character. Thus, to be "spineless" is to be without that essential core of strength, rendering one weak and easily bent to the will of others.

Structure: spine (backbone) + less (without) spine: From Latin spina (thorn, backbone). Functions as the core noun root denoting a backbone or central support. less: From Old English -lēas (devoid of, free from). Functions as a suffix forming adjectives meaning "without" the thing denoted by the root.