flimsy

Describes something that lacks the necessary strength to fulfill its purpose, whether physically or logically. It carries a strong connotation of disappointment or insufficiency; it is not just "thin," but inadequately thin. In physical contexts, it suggests a cheapness of material or poor craftsmanship. While "fragile" implies something delicate (like a crystal vase), "flimsy" implies something that should be sturdy but isn't (like a cheap plastic chair). When applied to arguments or excuses, it describes a lack of substance. A flimsy excuse is one that is so transparently weak that it is easily seen through, evoking a sense of desperation or dishonesty.