syllabise vs sound out

syllabise and sound out both are verbs.

Word	Noun	Adjective	Verb	Adverb
syllabise	No	No	Yes	No
sound out	No	No	Yes	No

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

Other hypernyms of syllabise include articulate, enounce, enunciate, pronounce, say.

syllabise (verb)	sound out (verb)
utter with distinct articulation of each syllable	try to learn someone's opinions and intentions
divide into syllables	speak, pronounce, or utter in a certain way