overturn vs turn turtle

overturn is a noun but turn turtle is not a noun.

Word	Noun	Adjective	Verb	Adverb
overturn	Yes	No	Yes	No
turn turtle	No	No	Yes	No

As verbs, turn turtle is a hyponym of overturn; that is, turn turtle is a word with a more specific, narrower meaning than overturn:

Other hyponyms of overturn include capsize, turtle, upend.

overturn (noun)	turn turtle (noun)
the act of upsetting something
an improbable and unexpected victory

overturn (verb)	turn turtle (verb)
change radically	overturn accidentally
rule against
cancel officially
turn from an upright or normal position
cause to overturn from an upright or normal position
cause the downfall of; of rulers