feeble
Very weak and not strong or convincing.
Feeble means physically weak or lacking strength and force. When someone feels feeble after being sick in bed for a week, their muscles feel shaky and tired, like their body has forgotten how to work properly. An elderly person might make a feeble attempt to open a stuck jar, their hands trembling with the effort.
The word also describes things that are weak or unconvincing in quality or effect. A feeble excuse for not doing homework sounds thin and unbelievable: “My dog ate it” is the classic feeble excuse. A feeble joke barely gets a chuckle. A feeble light barely illuminates a room.
When you call an argument feeble, you mean it lacks force or logic. If someone claims they should be class president because they have nice sneakers, that's a pretty feeble argument. The word suggests something so weak it almost isn't worth considering. A feeble protest is one that nobody really takes seriously. A feeble response to a challenge shows you're not putting in real effort.
Feeble carries a sense of something being disappointingly inadequate. It's usually not a compliment.