From Longman Dictionary of Contemporary Englishplead ignorance/illness/insanity etcplead ignorance/illness/insanity etcformalREASON to give a particular excuse for your actions She stayed home from work, pleading illness. → plead
Examples from the Corpus
plead ignorance/illness/insanity etc• The next day, she stayed home from work, something she rarely did, pleading illness.• As to his reference to rugby league, I plead ignorance and will not interfere with private griefs.• He attempted to plead insanity, but did it so effectively that they concluded he must be sane.• Galileo pleaded ignorance of any such document and promised to produce that signed by Bellarrnine in 1616.• In Seville he had often pleaded ignorance over some of the expressions she used. 