desertion vs defection

desertion and defection both are nouns.

Word	Noun	Adjective	Verb	Adverb
desertion	Yes	No	No	No
defection	Yes	No	No	No

As nouns, desertion and defection are synonyms defined as:

desertion and defection: withdrawing support or help despite allegiance or responsibility

Other synonyms of desertion include abandonment.

desertion (noun)	defection (noun)
withdrawing support or help despite allegiance or responsibility	withdrawing support or help despite allegiance or responsibility
the act of giving something up	the state of having rejected your religious beliefs for your political party or a cause (often in favor of opposing beliefs or causes)