adj

• Not permitting water or some other liquid to escape or penetrate; watertight.
  "[T]vvas very difficult to procure a Bladder ſmall and fine enough for that litle Cylinder; and that one, vvhich at length vve procured, vvould not continue ſtanch for many Tryals, but vvould after a vvhile part vvith a litle Air in the vvell exhauſted Receiver, vvhen tvvas clog'd vvith the utmoſt VVeight it could ſuſtain: but vvhilſt it continued ſtanch vve made one fair Tryal vvith it, […]"
• (figuratively)
  "Without our staunch front line the enemy would have split the regiment."
• (figuratively)
  "He’s been a staunch supporter of mine through every election."
• (figuratively)
  "[T]he horſemen & huntſmen ſhould blemiſh at ſuch places as they ſee the Hart enter into a thicket or couert to the end that if the hounds fall to change, they may return to thoſe blemiſhes, and put their hounds to the right ſlot and view, vntill they haue rowzed or found him againe with their bloudhound, or with ſome other ſtanch old hound of the kennell, in the which they may aſſie themſelues. For old ſtaunch houndes which will not hunt change, when they ſee an Hart rowzed & before them, they neuer call on, nor once open: but if they be young raſh houndes, they will runne with full cry & ſo take change."

noun

• (obsolete) That which stanches or checks a flow.
• (obsolete) That which stanches or checks a flow.
• (obsolete) An act of stanching or stopping.
• (mining) Synonym of afterdamp (“suffocating gases present in a coal mine after an explosion caused by firedamp”).