The Collaborative International Dictionary of English v.0.48:

Lab \Lab\, v. i. [Cf. OD. labben to babble.]
   To prate; to gossip; to babble; to blab. [Obs.] --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

lab \lab\, n.
   1. A telltale; a prater; a blabber. [Obs.] "I am no lab."
      --Chaucer.
      [1913 Webster]

   2. [By truncation of laboratory.] Laboratory. [Colloq.]
      [PJC]

The Collaborative International Dictionary of English v.0.48:

lab \lab\, a.
   Of or pertaining to a laboratory; as, a lab bench. [Colloq.]
   [PJC]