tact·ful (t?kt?f?l)adj. Possessing or exhibiting tact; considerate and discreet: a tactful person; a tactful remark.tact?ful·ly adv.tact?ful·ness n.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.