adj. tembloroso, convulsivo, convulso, en tanganillas, tambaleante, tembleque, vacilante

The following video provides you with the correct English pronunciation of the word "shaky", to help you become a better English speaker.

inseguro | inestable | tambaleante | tembloroso | cuestionable | precario

(adj.) = débil, precario, inestable.
Ex: The subdivision 'Discovery and Exploration' under geographic names reinforces the popularly held notion that the world outside Western Europe had no history -- and only a shaky hold on existence -- before it was 'discovered' by Western Europeans.
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* on shaky grounds = en terreno peligroso.