What is "main-topmast"

Usage examples of "main-topmast".

Next came a sudden succession of noises, all loud, all different, distinguishable even though not two seconds elapsed between the first and the last - the shriek of a shell, a crash of timber aloft, a deep note as the main-topmast backstay parted, a thud against the hammock nettings beside Hornblower, and then a thump three yards from his feet, and there on the deck death, sizzling death, was rolling towards him and as the ship heaved death changed its course with the canting of the deck in a blundering curve as the belt round the shell deflected its roll.