yammer vs sound off

yammer and sound off both are verbs.

Word	Noun	Adjective	Verb	Adverb
yammer	No	No	Yes	No
sound off	No	No	Yes	No

As verbs, sound off is a hypernym of yammer; that is, sound off is a word with a broader meaning than yammer:

Other hypernyms of yammer include complain, kick, kvetch, plain, quetch.

yammer (verb)	sound off (verb)
complain whiningly	express complaints, discontent, displeasure, or unhappiness
cry loudly, as of animals	express one's opinion openly and without fear or hesitation
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