Ontic and ontological both relate to being, but in distinct ways.
Since Heidegger, ontic refers to beings — concrete, perceived, determined entities — while ontological refers to Being itself, the ground or meaning of being.

More precisely

The term ontic (from Greek to on: the being, the existent) designates whatever concerns particular entities, their characteristics, relations, and determinations.
The ontic level deals with what is there: things, events, persons, situations.

The term ontological, by contrast, refers to Being as such — the meaning, structure, and conditions of possibility of being.
The ontological does not study this or that being, but Being as what enables beings to be.

In Heidegger’s terms:
— the ontic concerns beings (Seiendes),
— the ontological concerns Being (Sein).

Thus, one can conduct an ontic investigation of facts, sciences, or objects, but the ontological question is:

What is Being?

For classical metaphysics (Plato, Aristotle, Thomas Aquinas), the ontological inquiry is fundamental:
it concerns the act of being, essence, substance, and first causes.

Heidegger introduces an existential analytic of the human being (Dasein), the only being able to question Being.
Ontically, Dasein is a living human; ontologically, it is characterized by structures such as being-in-the-world, being-toward-death, etc.

A common confusion is to call ontological what is merely descriptive.
The ontological is about the ground of possibility, not factual detail.

For further reading

  • Plato, Sophist — On the distinction between being and beings.
  • Aristotle, Metaphysics — Science of being as being.
  • Thomas Aquinas, De ente et essentia — Distinction between essence and act of being.
  • Martin Heidegger, Being and Time (1927) — Foundational distinction: ontic / ontological; analysis of Dasein.
  • Jean Beaufret, Dialogue avec Heidegger — On Heidegger’s ontological thought.
  • Bruno Bérard, Metaphysics for Everyone (Angelico Press);
    — fr. Métaphysique pour tous (Paris, L’Harmattan, 2022)
    — it. Sui sentieri della metafisica
    — es. ¿Qué es la metafísica?
    — de. Was ist Metaphysik?
    On being, its degrees, and ontological hierarchy.