shaky
Unsteady, weak, or likely to fail or fall.
Shaky means unsteady or unstable, like when your hands tremble after you've been nervous or when a wobbly table rocks back and forth. If you're feeling shaky after running a long race, your legs might feel weak and unreliable. A ladder that feels shaky makes you worry it might tip over.
The word also describes things that aren't physically trembling but seem uncertain or unreliable. A student might have a shaky understanding of fractions, meaning they sort of get it but couldn't explain it clearly or solve harder problems. A plan seems shaky when it has obvious flaws that could cause it to fail. When someone gets off to a shaky start learning to ride a bike, they wobble and struggle at first.
People sometimes feel shaky when they're scared, sick, or exhausted. Your voice might sound shaky when you're about to cry or when you're standing in front of the class giving a presentation. Shaky hands or a shaky voice can reveal what someone's feeling inside, even when they're trying to appear calm and confident on the outside.