speak up vs speak

speak up and speak both are verbs.

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

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

Other hypernyms of speak up include mouth, talk, utter, verbalise, verbalize.

speak up (verb)	speak (verb)
express one's opinion openly and without fear or hesitation	express in speech
speak louder; raise one's voice	exchange thoughts; talk with
	use language
	give a speech to
	make a characteristic or natural sound