What is the prefix in the word apology, and what does it mean?

Random House Dictionary (available at Dictionary.com)
gives the etymology of apology
as:

1400–50;
earlier apologie, late ME apologe (< MF) < LL apologia < Gk; see
apologia

This means that the
original source of the word was the underived (i.e., no prefixes or suffixes) Greek word
apologia. It was then borrowed as a
loanword into Late Latin and used in its Greek form
apologia. From Latin, the word was
next borrowed as a loanword into Middle French in the same form and from there borrowed
into late Middle English (around Chaucer's time) as
apologe, manifesting the first change
in form from the original Greek word. Finally between 1400 and 1450 the first evidence
of the English variation of apologie
appears in a written source. From this etymology, you can see that
apology is not a
derived word built from a root and prefix nor a combined
word built from Greek or Latin combining forms.

Therefore
the prefix apo- is not part of
apology. However, also according to
Random House Dictionary, the prefix
apo- (variation
ap-) is a Greek prefix used on verbs
to derive nouns like apogee and verbs
like apoplexy. The
apo- prefix conveys a spatial sense
described by the prepositions away
or apart. In
cases like this, checking for the etymology of a word will
tell you whether it is a derived word with prefix and/or suffix or whether it is a root
word itself or some other word form. Also, greater acquaintance with root words will
expand your knowledge of the etymology of words.