- noun one of the signs of the Zodiac, shaped like twins, covering the period 21st May to 21st June
- constellation of the Zodiac in the northern hemisphere. Meaning the twins, Gemini is best known for the bright stars Castor and Pollux, representing the mythical twins.
- US two-man spacecraft programme, carried out between 1961 and 1963
- US/European project to build two 8.1m telescopes on Hawaii and at Cerro Pachon in Chile. Both telescopes came into operation in 2000.