laugh vs laugh softly

laugh is a noun but laugh softly is not a noun.

Word	Noun	Adjective	Verb	Adverb
laugh	Yes	No	Yes	No
laugh softly	No	No	Yes	No

As verbs, laugh softly is a hyponym of laugh; that is, laugh softly is a word with a more specific, narrower meaning than laugh:

laugh (noun)	laugh softly (noun)
the sound of laughing
a humorous anecdote or remark intended to provoke laughter
a facial expression characteristic of a person laughing

laugh (verb)	laugh softly (verb)
produce laughter	laugh quietly or with restraint