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[L. tonus, a stretching]

1. That state of a body or any of its organs or parts in which the functions are healthy and normal. In a more restricted sense, the resistance of muscles to passive elongation or stretch.
2. Normal tension or responsiveness to stimuli, as of arteries or muscles, seen particularly in involuntary muscle (such as the sphincter of the urinary bladder).
SYN: SEE: tonicity (2). A musical or vocal sound.

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