event vs side effect

event and side effect both are nouns.

Word	Noun	Adjective	Verb	Adverb
event	Yes	No	No	No
side effect	Yes	No	No	No

As nouns, side effect is a hyponym of event; that is, side effect is a word with a more specific, narrower meaning than event:

event (noun)	side effect (noun)
something that happens at a given place and time	any adverse and unwanted secondary effect
a phenomenon located at a single point in space-time; the fundamental observational entity in relativity theory	a secondary and usually adverse effect of a drug or therapy
a phenomenon that follows and is caused by some previous phenomenon
a special set of circumstances