Meaning
Unsteady, unreliable, or not to be trusted — of a person, plan, or thing you can't depend on. A 'shakey' character might let you down or turn out crooked; a 'shakey' arrangement is precarious and likely to fall apart. Beyond the literal 'trembling' sense.
Examples
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Di deal look shakey, mi nuh trust it.
The deal looks shaky, I don't trust it.
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Him too shakey, him will let yuh down.
He's too unreliable, he'll let you down.
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Di whole plan shakey from start.
The whole plan was precarious from the start.
Origin
From 'shaky' (unsteady/trembling), extended to 'unreliable/untrustworthy'.
How it’s used
Unreliable/untrustworthy/precarious. Compare 'sometime-ish', 'wamp'.