Critically for Seriously. "He has long been critically ill." A patient is critically ill only at the crisis of his disease.
Criticise for Condemn, or Disparage. Criticism is not necessarily censorious; it may approve.
Cunning for Amusing. Usually said of a child, or pet. This is pure Americanese, as is its synonym, "cute."
Curious for Odd, or Singular. To be curious is to have an inquiring mind, or mood—curiosity.
Custom for Habit. Communities have customs; individuals, habits—commonly bad ones.
Decease for Die.
Decidedly for Very, or Certainly. "It is decidedly cold."
Declared for Said. To a newspaper reporter no one seems ever to say anything; all "declare." Like "alleged" (which see) the word is tiresome exceedingly.
Defalcation for Default. A defalcation is a cutting off, a subtraction; a default is a failure in duty.
Definitely for Definitively. "It was definitely decided." Definitely means precisely, with exactness; definitively means finally, conclusively.