These words refer to anything slight, weak, thin or sheer and thus either lacking in permanence or vulnerable to damage or criticism. Flimsy is the most general in embodying all these meanings, particularly emphasizing a lack of density that makes for limpness rather than rigidity: flimsy cloth that clung to the outlines of her body; a flimsy stalk that caused the flower to droop in its vase. Less concretely used, the word may refer to inferior materials, worthlessness, implausibility or low standards: flimsy books that come apart in your hands; the flimsy reporting of the local newspaper; a flimsy excuse; a flimsy , meretricious play. Frail , by contrast, concentrates more on slenderness, weakness or enfeeblement: furthermore, it need not suggest limpness: the frail filaments used in light bulbs; the frail teacup of bone china; a disease that left him frail from loss of weight. Flimsy suggests, also, possible damage through tearing, frail through breaking or shattering. Used more metaphorically, frail does not function with the same intensity of disapproval felt in flimsy , although it can give a negative tone: a grasp of orchestration too frail to give his symphonic ideas convincing weight. More often, however, the word can render a sharply contrasted connotation of pity: frail hopes long ago shattered by the brutal facts of slum life.

Like frail , tenuous can emphasize thinness, although in this case weakness is not necessarily involved: a heavy free-floating sculpture hung from tenuous wires that made it seem light and airy. The word’s particular relevance, however, is to haziness: a tenuous fog that threatened to thicken by morning. Related to this possibility is its more metaphorical suggestion of vagueness or confusion: ideas too tenuous to result in a realistic research project. Unsubstantial is the most formal of these words and emphasizes a lack of density, firmness, permanence or stability: building houses out of paper and other unsubstantial materials. Less specifically, the word points to something that is without basis in fact, cannot pass inspection, or that partakes of fancy or fantasy: unsubstantial theories; unsubstantial grounds for an appeal to a higher court; unsubstantial dreams of escaping her dreary existence.