The word 'squalid' originates from the Latin verb squalere, which meant to be stiff, rough, or, by extension, filthy. This Latin root is thought to be related to squalus, meaning a kind of shark or a type of fish with rough skin, metaphorically evoking a sense of coarseness and neglect. Over time, the primary sense of dirtiness and physical neglect became firmly attached to the adjective 'squalidus' in Latin. Entering English in the late 16th century, 'squalid' retained this core meaning of being filthy and wretched from poverty, and later developed a secondary, figurative sense describing actions or situations that are morally degraded or sordid.

Structure: squal (dirty) + id (adjective suffix) - squal: From Latin squalere (to be stiff, rough, or filthy). - id: A suffix forming adjectives, often from Latin -idus, indicating a state or condition.