Definition of breastsummer in English:

breastsummer

noun

Architecture
  • A beam across a broad opening, sustaining a superstructure.

    • ‘There is an exquisite little parlour, lined with linen fold panels, with a breastsummer carved with strange animals.’

Origin

Early 17th century: from breast and summer.

Pronunciation:

breastsummer

/ˈbrɛs(t)sʌmə/