daddy longlegs vs Phalangium opilio

daddy longlegs and Phalangium opilio both are nouns.

Word	Noun	Adjective	Verb	Adverb
daddy longlegs	Yes	No	No	No
Phalangium opilio	Yes	No	No	No

As nouns, daddy longlegs and Phalangium opilio are synonyms defined as:

daddy longlegs and Phalangium opilio: spiderlike arachnid with a small rounded body and very long thin legs

Other synonyms of daddy longlegs include harvestman.

daddy longlegs (noun)	Phalangium opilio (noun)
long-legged slender flies that resemble large mosquitoes but do not bite	spiderlike arachnid with a small rounded body and very long thin legs
spiderlike arachnid with a small rounded body and very long thin legs