soften vs tone down

soften and tone down both are verbs.

Word	Noun	Adjective	Verb	Adverb
soften	No	No	Yes	No
tone down	No	No	Yes	No

As verbs, tone down is a hyponym of soften; that is, tone down is a word with a more specific, narrower meaning than soften:

Other hyponyms of soften include damp, dampen, dull, muffle, mute.

soften (verb)	tone down (verb)
become soft or softer	make less strong or intense; soften
make soft or softer	deaden (a sound or noise), especially by wrapping
lessen in force or effect
make less severe or harsh
protect from impact
make (images or sounds) soft or softer
give in, as to influence or pressure