al·the·a also al·thae·a (?l-th???)n.1. See rose of Sharon.2. See hollyhock.[Latin, mallows, from Greek althaia, from althainein, to heal; see al- in Indo-European roots.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.al?the?a or al?thae?a (æl??i ?) n., pl. -the?as or -thae?as. 1. the rose of Sharon, Hibiscus syriacus. 2. any plant belonging to the genus Althaea, of the mallow family, having lobed leaves and showy flowers in a spikelike cluster, including the hollyhocks and marsh mallows. [1660?70;