To a great extent; very much: Would you mind terribly if I opened the window? (adverb)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "terribly" in a sentence
"It was small-minded and petty and terribly, terribly wrong of me to misjudge you."
"“I know what you mean,” Sisko said, assuming that she referred to the terribly misguided Winn Adami."
"And yet the men are in terribly wretched condition."