The Collaborative International Dictionary of English v.0.48:

Tincal \Tin"cal\, n. [Ar., Per. & Hind. tink[=a]r; cf. Malay
   tingkal; all fr. Skr. ?a?ka?a. Cf. Altincar.] (Chem.)
   Crude native borax, formerly imported from Thibet. It was
   once the chief source of boric compounds. Cf. Borax.
   [1913 Webster]