D defs.my
Entry 2 senses Webster, 1913

Mainstay

/mān'-stāˌ/ · Main·stay · IPA /ˈmeɪn.steɪ/
01 n. The stay extending from the foot of the foremast to the maintop.
  1. 1.
    The stay extending from the foot of the foremast to the maintop.(Naut.)
  2. 2.
    Main support; principal dependence.
    “The great mainstay of the Church.” — Buckle.