- cygnet: A young swan.
- cynical: Exhibiting moral skepticism.
- cynicism: Contempt for the opinions of others and of what others value.
- cynosure: That to which general interest or attention is directed.
- daring: Brave.
- darkling: Blindly.
- Darwinism: The doctrine that natural selection has been the prime cause of evolution of higher forms.
- dastard: A base coward.
- datum: A premise, starting-point, or given fact.
- dauntless: Fearless.
- day-man: A day-laborer.
- dead-heat: A race in which two or more competitors come out even, and there is no winner.
- dearth: Scarcity, as of something customary, essential ,or desirable.
- death's-head: A human skull as a symbol of death.
- debase: To lower in character or virtue.
- debatable: Subject to contention or dispute.
- debonair: Having gentle or courteous bearing or manner.
- debut: A first appearance in society or on the stage.
- decagon: A figure with ten sides and ten angles.
- decagram: A weight of 10 grams.
- decaliter: A liquid and dry measure of 10 liters.
- decalogue: The ten commandments.
- Decameron: A volume consisting of ten parts or books.
- decameter: A length of ten meters.
- decamp: To leave suddenly or unexpectedly.
- decapitate: To behead.
- decapod: Ten-footed or ten-armed.
- decasyllable: A line of ten syllables.
- deceit: Falsehood.
- deceitful: Fraudulent.
- deceive: To mislead by or as by falsehood.
- decency: Moral fitness.
- decent: Characterized by propriety of conduct, speech, manners, or dress.
- deciduous: Falling off at maturity as petals after flowering, fruit when ripe, etc.
- decimal: Founded on the number 10.
- decimate: To destroy a measurable or large proportion of.
- decipher: To find out the true words or meaning of, as something hardly legible.
- decisive ad: Conclusive.
- declamation: A speech recited or intended for recitation from memory in public.
- declamatory: A full and formal style of utterance.
- declarative: Containing a formal, positive, or explicit statement or affirmation.
- declension: The change of endings in nouns and adj. to express their different relations of gender.
- decorate: To embellish.
- decorous: Suitable for the occasion or circumstances.
- decoy: Anything that allures, or is intended to allures into danger or temptation.
- decrepit: Enfeebled, as by old age or some chronic infirmity.
- dedication: The voluntary consecration or relinquishment of something to an end or cause.
- deduce: To derive or draw as a conclusion by reasoning from given premises or principles.
- deface: To mar or disfigure the face or external surface of.
- defalcate: To cut off or take away, as a part of something.