n. A platform at the top of a square-rigged vessel's mainmast; used for observation and for the attachment of rigging.
the GNU version of the Collaborative International Dictionary of English
n. The platform about the head of the mainmast in square-rigged vessels.
The Century Dictionary and Cyclopedia
n. Nautical, a platform just below the head of the mainmast, resting on the trestletrees. See top.
Word Usage
"Larkyns at the maintop was a good second, while Adams at the mizzen was the last; the officer of the watch, on hearing his hail, reporting "All ready!""