about vs close to

about is an adjective but close to is not an adjective.

Word	Noun	Adjective	Verb	Adverb
about	No	Yes	No	Yes
close to	No	No	No	Yes

As adverbs, about and close to are synonyms defined as:

about and close to: (of quantities) imprecise but fairly close to correct

Other synonyms of about include approximately, around, just about, more or less, or so, roughly, some.

about (adjective)	close to (adjective)
on the move

about (adverb)	close to (adverb)
(of quantities) imprecise but fairly close to correct	(of quantities) imprecise but fairly close to correct
in the area or vicinity
in or to a reversed position or direction
in rotation or succession
used of movement to or among many different places or in no particular direction
(of actions or states) slightly short of or not quite accomplished; all but
all around or on all sides