The Collaborative International Dictionary
Top-block
Top-block \Top"-block`\, n. (Naut.)
A large ironbound block strapped with a hook, and, when used,
hung to an eyebolt in the cap, -- used in swaying and
lowering the topmast.
--Totten.
Wiktionary
top-block
n. (context nautical English) A large ironbound block strapped with a hook, and, when used, hung to an eyebolt in the cap, used in swaying and lowering the topmast.