From The Collaborative International Dictionary of English v.0.48 :
vitamin B \vitamin B\ n. a group of water-soluble vitamins originally thought to be a single vitamin but now separated into several B vitamins. Syn: B-complex vitamin, B complex, vitamin B complex, B vitamin. [WordNet 1.5]From WordNet (r) 3.0 (2006) :
vitamin B n 1: originally thought to be a single vitamin but now separated into several B vitamins [syn: B-complex vitamin, B complex, vitamin B complex, vitamin B, B vitamin, B]