nisus

Etymology
From.

Noun

 * 1) A mental or physical effort to attain a specific goal; a striving.
 * 2) The periodic procreative desire manifested in the spring by birds, etc.
 * 3) The contraction of the diaphragm and abdominal muscles to evacuate faeces or urine.
 * 4) * 1833, James O' Beirne, New Views on the Process of Defecation, and Their Application to the Pathology and Treatment of Diseases of the Stomach, Bowels, and Other Organs, quoted in 1833, John Johnson (editor), The Medico-Chirurgical Review, New Series: Volume 19 (Volume 23 of the Analytical Series), page 7,
 * The evacuation of the rectum and bladder being completed, immediately the nisus ceases, the rectum and the sphincters return to their former state of contraction, the diaphragm reascends, carrying with it and restoring to their proper situations the liver, the stomach, the spleen, the small intestines, the cæcum, and the ascending, transverse and descending portions of the colon.
 * 1) * 1833, James O' Beirne, New Views on the Process of Defecation, and Their Application to the Pathology and Treatment of Diseases of the Stomach, Bowels, and Other Organs, quoted in 1833, John Johnson (editor), The Medico-Chirurgical Review, New Series: Volume 19 (Volume 23 of the Analytical Series), page 7,
 * The evacuation of the rectum and bladder being completed, immediately the nisus ceases, the rectum and the sphincters return to their former state of contraction, the diaphragm reascends, carrying with it and restoring to their proper situations the liver, the stomach, the spleen, the small intestines, the cæcum, and the ascending, transverse and descending portions of the colon.

Etymology 1
From.

Noun

 * 1) pressure downward push
 * 2) exertion

Etymology 2
Perfect participle of.

Etymology 3
From.

Noun

 * 1) sea-eagle
 * 2) sparrowhawk