These words refer to things easily broken. Fragile , beyond this general meaning, may suggest weakness or delicacy as well: a fragile teacup; the shipping of fragile materials; her fragile health; a lovely, fragile embroidery of flower motifs. Frail carries its own implication of slenderness or enfeeblement, as well as of breakability or weakness: a frail scaffold; frail columns bearing the architrave; made frail by persisting bouts of malaria.

Brittle , like fragile, need not suggest slightness or slenderness, and it is also less apt than either of the previous words to indicate weakness or delicacy of construction. It refers to any hard material that tends to shatter easily under a direct impact: Glass is brittle, choosing building stones less brittle than marble or granite. More metaphorically, it contrasts sharply with the softness that may be implied by frail , suggesting instead a hard, brusque manner or appearance: giving him a brittle , contemptuous reply.

The remaining words are considerably more formal than the foregoing and are also much more specific in meaning. Frangible may be used only to indicate breakability; but, more relevantly here, it is often applied to materials specifically designed to be broken: a frangible capsule of ammonia that is broken and held under the fainting person’s nose. Friable is even more restricted in meaning, referring exclusively to materials that can be easily crumbled: sandstone slabs that are not brittle but tend to be friable . Occasionally the word can refer to anything vulnerable to being worn down: topsoil made less friable by the planting of trees.