Astr

Astr is a combining form used in English to denote relation to stars. It derives from the Greek word astron meaning star and entered English through Latin and later scientific vocabulary. In contemporary usage the form appears in two spellings, astr- and astro-, and is productive in many star-related terms.

Common derivatives include astronomy, astronomer, and astronomical, which refer to the science of celestial objects, their properties, and their observation. The adjective astral, meaning pertaining to the stars or to a non-physical plane, also derives from the same root. In space exploration and related fields, terms such as astronaut and astronautics use the root to denote persons and technologies associated with space travel. The prefix astro- is especially widespread in modern coinages across disciplines, from astrophysics to astrology and beyond.

Related forms include aster- words such as asteroid and asterism, which come from a closely related root meaning star. While astr/astro is primarily associated with stars, the broader family of terms reflecting celestial phenomena spans several morphologies and languages. In usage, astr/astro- remains a foundational element in science, culture, and literature when describing stars, space, and star-like appearances.