Something that cannot be found, noticed, or discovered because it is too small, hidden, or well-concealed.
Prefix 'un-' (not) combined with 'detectable' (able to be found), 'detect' comes from Latin 'detectus' (uncovered).
In medicine, 'undetectable viral load' means HIV in a patient's body is so low it can't transmit—a huge breakthrough that changed how we think about the disease and treatment.
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