Self is a pronoun used to refer to a person in a general sense. It is most commonly heard in myself, herself, or himself.
As a prefix, it means the action or quality or object is given to one’s self or done toward one’s self. The vast majority of the time, self- words use a hyphen (e.g., self-love, self-actualization, or self-absorbed).
In fact, with the exception of selfish, selfsame, selfness, selfless, and selfhood, all self- words hyphenated. Notice in the list of exceptions that all but one are suffixes.
Selfsame is an adjective that describes someone or something as identical to a prior time or condition, or in other words, the object or person has not changed in the slightest manner.
This does have a noun form, selfsameness.
The great question that lurks at the heart of all Holocaust study, it seems to me, is the question of the self. [Truthout]
Nissan will be ready for its self-driving vehicles to roll out as early as 2020 — but one major roadblock is standing in the way: Regulators. [ABC News]
Brexit without a balanced argument would have a crucifying cost, mostly borne by those selfsame voters. [The Telegraph]
For them, all time runs off aimlessly into a sea of selfsameness that only duplicates the mediocrity that is in plentiful supply, which (inexplicably) they are always in a hurry to do — they are the ones who are always passing in their cars: they are not going anywhere, they simply must be “ahead.” [Inman]