whisper vs speak

whisper is a noun but speak is not a noun.

Word	Noun	Adjective	Verb	Adverb
whisper	Yes	No	Yes	No
speak	No	No	Yes	No

As verbs, speak is a hypernym of whisper; that is, speak is a word with a broader meaning than whisper:

Other hypernyms of whisper include mouth, talk, utter, verbalise, verbalize.

whisper (noun)	speak (noun)
speaking softly without vibration of the vocal cords
a light noise, like the noise of silk clothing or leaves blowing in the wind

whisper (verb)	speak (verb)
speak softly; in a low voice	express in speech
	exchange thoughts; talk with
	use language
	give a speech to
	make a characteristic or natural sound