inˌvisible ˈink BrE AmE noun [uncountable]
ink that cannot be seen on paper until it is heated, treated with chemicals etc, and is used for writing secret messages
inˌvisible ˈink BrE AmE noun [uncountable]
ink that cannot be seen on paper until it is heated, treated with chemicals etc, and is used for writing secret messages
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012