The Collaborative International Dictionary of English v.0.48:
pachytene \pachytene\ n. (Biol.) The third stage of the prophase of meiosis, the stage in which the pairing of homologous chromosomes has been completed. [WordNet 1.5]WordNet (r) 3.0 (2006):
pachytene n 1: the third stage of the prophase of meiosis