THISTLEDOWN Meaning of THISTLEDOWN in English this ‧ tle ‧ down /ˈθɪs ə ldaʊn/ BrE AmE noun [uncountable] the soft feathery substance fastened to thistle seeds that helps them to float in the air Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012