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The Collaborative International Dictionary of English v.0.48 (gcide)

Macho \Ma"cho\, n. [Sp.] (Zool.)
The striped mullet of California ({Mugil cephalus}, syn.
{Mugil Mexicanus}).
[1913 Webster PJC]


macho \ma"cho\, a. [Sp.]
Manly, especially with an assertive and domineering manner
toward women.
[PJC]


MACHO \MACHO\ (m[aum]"k[-o]), n. [acronym from Massive
Astrophysical Compact Halo Object.]
A form of dark matter in distant outer space unobservable
except by its gravitational effect, and believed to be at
least part of the "missing matter" which is unobservable as
ordinary stars, but helps keep galaxies from flying apart;
MACHOS are massive but compact objects such as neutron stars
or brown dwarfs, which can be detected (with difficulty) by
their effect in bending light from distant light sources,
such as other galaxies. This can occur if by rare chance a
MACHO passes in front of a more distant visible object, and
the light from that object becomes temporarily amplified by
the MACHO acting as a gravitational lens. Some MACHOs have
been discovered in the halo of dark matter that surrounds our
milky way. It is, however, questionable whether the amount of
such matter is sufficient to explain the ability of galaxies
to stay together in spite of rotation rates that would cause
them to fly apart if the only matter present was that
observable as visible stars.
[PJC]