A.C. or A.C.N.
From Latin Ante Christum or Ante Christum Natum, meaning "Before Christ" or "Before Christ (was) Born." B.C. and B.C.E. are equivalents.
A.D.
From Latin Anno Domini, meaning "in the year of the Lord." C.E. is equivalent.
A.K.A.
From also known as.
A.M.
From Latin Ante Meridiem, meaning "before midday."
A.S.A.P.
From as soon as possible.
attn.
From attention.
AWOL
From absent without leave.
B.C.
From Before Christ. A.C.N. and B.C.E. are equivalents.
B.C.E.
From Before Common Era. A.C.N. and B.C. are equivalents.
C.E.
From Common Era. A.D. is equivalent.
co.
From county.
cf.
From confer, meaning "compare" or "consult." Cf. refers to additional material or ideas providing further information.
ed.
From edited, edition, or editor(s).
e. g.
From Latin exempli gratia, meaning "for (the sake of) example." E.g. introduces one or more examples.
est.
From established or estimated.
et al.
From Latin et alii, meaning "and others."
etc.
From Latin et cetera, meaning "and so forth."
i.a.
From Latin inter alia, meaning "among other things."
ibid.
From Latin ibidem, meaning "the same place." Ibid. refers to an endnote or footnote citation that was cited in the preceding endnote or footnote.
id.
From Latin idem, meaning "the same (man)." Id. replaces the name of a repeated author in academic citations and refers to the previously cited source in legal citations.
i.e.
From Latin id est, meaning "that is" (to say). I.e. precedes a clarification or restatement and can also be used to mean "in other words" or "in this case."
i.f.
From Latin in fine, meaning "in the end." I.f. may be used with a citation to indicate the cited material's location at the bottom of the page or "at the end."