- a stay, or line, extending forward from the mainmast, supporting it and holding it in position
- a chief support
The definition of a mainstay is something that is depended on, or something that is necessary.
Fruits and vegetables are an example of the mainstay of a healthy diet.
- A chief support: Agriculture is a mainstay of the economy.
- Nautical A stay running forward from the mainmast to the deck of a sailing vessel.
- Fishing is the occupation of the men, and the real mainstay of the inhabitants.
- That this doctrine was a mainstay of Jewish faith in those very days of exile which gave the Sabbath a new importance for the faithful.
- In the latter year the imports amounted to £467,000, and the exports to £451,000; coffee, the mainstay of Yemen trade, shows a serious decline from £302,000 in 1902 to £229,000 in 1904; this is attributable partly to the great increase of production in other countries, but mainly to the insecurity of the trade routes and the exorbitant transit dues levied by the Turkish administration.
- His friend and instructor, Bernard of Clairvaux, the most influential ecclesiastic of the time, remonstrated against his election on account of his "innocence and simplicity," but Bernard soon acquiesced and continued to be the mainstay of the papacy throughout Eugenius's pontificate.
- The political mainstay of the papacy, had never abandoned the broad lines of ecclesiastical policy laid down by Joseph II.; but the young Francis Joseph, seeking the aid of Rome in curbing heterogeneous nationalities, in 1855 negotiated a concordat whose paragraphs regarding the censorship, education and marriage were far-reaching.