RichThesaurus
a's
a's
synonyms
As
after noting that the usage has changed
states on page 602 that The 15th edition of The Chicago Manual of Style states in paragraph 7.16
A's
as
aes
lowercase letters ... form the plural with an apostrophe and an s". The Oxford Style Manual on page 116 advocates the use of common sense.
"To avoid confusion
There is some difference of opinion regarding the use of apostrophes in the pluralization of references to letters as symbols. New Fowler's Modern English Usage
a's
antonyms