bee killer vs robber fly

bee killer and robber fly both are nouns.

Word	Noun	Adjective	Verb	Adverb
bee killer	Yes	No	No	No
robber fly	Yes	No	No	No

As nouns, bee killer and robber fly are synonyms defined as:

bee killer and robber fly: swift predatory fly having a strong body like a bee with the proboscis hardened for sucking juices of other insects captured on the wing

bee killer (noun)	robber fly (noun)
swift predatory fly having a strong body like a bee with the proboscis hardened for sucking juices of other insects captured on the wing	swift predatory fly having a strong body like a bee with the proboscis hardened for sucking juices of other insects captured on the wing