drop down vs drop open

drop down and drop open both are verbs.

Word	Noun	Adjective	Verb	Adverb
drop down	No	No	Yes	No
drop open	No	No	Yes	No

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

Other hyponyms of drop down include fall open, droop, flag, sag, swag, sag, sag down.

drop down (verb)	drop open (verb)
fall or descend to a lower place or level	open involuntarily