(chemistry) A zwitterion.

An inflatable rubber tube inserted into the casing of a pneumatic tyre/tire.

The mechanisms that function internally to a system and are not outwardly visible

Tending to follow one's own rules rather than those of society

Of, pertaining to, or situated in the central part of a city, especially an older, populous area of low-income or immigrant families.

(astronomy, planets) Any planet of the Solar System whose orbit is located between the asteroid belt and the sun, i.e., any of Mercury, Venus, Earth, or Mars.

(linear algebra) A generalization of the dot product for vectors of any dimensionality that may or may not be complex-numbered.

A nonviolent protester who participates in a sit-in.

Peace of mind.

(idiomatic) The group comprising one's closest friends or associates. / Used other than figuratively or idiomatically: see inner, circle.