trenchant -- Isabella

trench·ant  (trnchnt) adj. 1. Forceful, effective, and vigorous: a trenchant argument. See Synonyms at incisive. 2. Caustic; cutting: trenchant criticism. 3. Distinct; clear-cut. [Middle English, from Old French, cutting, from present participle of trenchier, to cut; see trench.] trenchan·cy n. trenchant·ly adv.

The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.

In debate, Isabella has learned to make a trenchant argument.