Synonyms vary by region:
卷心菜 (juǎnxīncài, lit. "rolled-heart vegetable") in northern China,
包菜 (bāocài) in central/south,
高丽菜 (gāolìcài) in Taiwan,
椰菜 (yēcài) in Cantonese.
甘蓝 is the formal/botanical term, with
甘蓝菜 a slightly more colloquial variant.