singly vs separately

singly and separately both are adverbs.

Word	Noun	Adjective	Verb	Adverb
singly	No	No	No	Yes
separately	No	No	No	Yes

As adverbs, singly and separately are synonyms defined as:

Other synonyms of singly include individually, on an individual basis, one by one, severally.

singly (adverb)	separately (adverb)
one by one; one at a time	apart from others
apart from others