Ni"sus (?), n. [L., fr. niti, p. p. nisus, to strive.]
A striving; an effort; a conatus.
A nisus or energizing towards a presented object.
Hickok.
© Webster 1913
Ni"sus (?), n. (Physiol.)
(a)
The periodic procreative desire manifested in the spring by birds, etc.
(b)
The contraction of the diaphragm and abdominal muscles to evacuate feces or urine.
© Webster 1913