retain vs hold down

retain and hold down both are verbs.

Word	Noun	Adjective	Verb	Adverb
retain	No	No	Yes	No
hold down	No	No	Yes	No

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

retain (verb)	hold down (verb)
keep in one's mind	restrain
secure and keep for possible future use or application	keep
allow to remain in a place or position or maintain a property or feature
hold back within