The description of the word you requested from the astronomical dictionary is given below.
When two heavenly bodies are in conjunction, then they are very close together in the sky. When astronomers say something like "Jupiter is in conjunction" without mentioning a second heavenly body, then they mean "with the Sun". In such a case Jupiter is not visible at any time of the night. The planets that are further away from the Sun than the Earth (the superior planets) have one conjunction each synodical orbital period. The planets that are closer to the Sun (the inferior planets, Mercury and Venus) have two conjunctions per synodical orbital period: one when they pass between the Sun and the Earth (the inferior conjunction), and one when they pass behind the Sun (the superior conjunction).