The present paper has dealt with the function and meaning of ``ac(앚)``, and some problems related to the formation and meaning of compound words with ``ac(앚)`` inside themselves. It could be explained that a form ``ac(앚)`` played a role of radical root, becoming affixed. It, as a radical root, takes on a group of meanings such as young, infantile, early, and as an affix, another group of meanings such as ``secondary-ness``, ``indirect-ness``. The list of compound words with ``ac(앚)`` shows itself as ``acy∂k(아젹), aspochi(앗보치), acapi(아자비)/acΛmi(아□미), acapa(아자바)/acΛma(아□마), *acap∂zi(아자버□)>acap∂i(아자버이), aci(아지)``, etc. Evidently though having the element ``ac``, seen from its semantics, ``acy∂k(morning) is difficult to analyse as morphological components. ``ac`` in ``acy∂k`` takes on the meaning of ``early``. ``aspochi``, composed of ``pachi`` and ``ac-`` as a prefix, denotes ``nephew``. (The etymology and meaning of ``pochi`` is not certain, but is said to have the meaning of ``kinship``. It is because ``ac-`` is prefixed as secondary or indirect marker to distinguish between ``pochi`` and close kinship members.) ``acapi(아자비)``. ``*acami(아자미) >acΛmi(아□미)`` could be analysed as basic roots ``api(아비, father)`` and ``*ami(아미, mother)`` and a prefix ``ac-`` to reveal distinctness. It follows that ``acipi`` denotes ``uncle`` on father`s side, and ``*acami>acΛmi``, ``aunt`` on mother`s side. These kinship terms ``acapa(아자바)``. ``*acama(아자마)>acΛma(아□마)`` are different from those ``acapi(아자비)``, ``*acami(아자미)>acΛmi(아□미)`` in that the former use the calling words ``apa(아마, father)``. ``*ama(아비, mother)`` while the latter use the designating words ``api(아비)``. ``*ami(아미)``. Now ``acapi`` remains as ``acupi(아주비)``, ``acΛmi(아□미)``, ``acumi(아주미)``, ``acama(아자마)``, ``acumma(아줌마)``, but ``acapa(아자바)`` has disappeared. ``*ac∂p∂zi(아저버□)>ac∂p∂i(아저버이)`` could be analysed as an affix ``ac(앚)-`` and a root ``∂p∂zi(어버□)`` referring to ``parents``. Thus, it designates uncle and aunt who rank as high as parents, but more secondary and indirect family members to parents. They belong to the same line as ``han∂p∂zi(한어버□)`` referring to ``grandparents``. ``ac∂p∂i(아저버이)``. ``han∂p∂i(한어버이)`` have been pushed out by Chinese words ``伯叔父母(uncle and aunt)``, ``祖父母(grandfather and grandmother)``. ``aci(아지)`` could be analysed as a root ``ac(앚)`` and a fuffix ``-i(이)``. That derived noun ``aci`` designates ``a younger person or animal``. It has become as a suffix referring to ``a little thing``, and it further takes some extra meaning of ``degradation`` or ``scorn``.