Is a cedar tree deciduous or conifer?

The two options are not comparable. The more accurate question is whether a cedar tree is deciduous or evergreen. Deciduous plants any plants that drop their leaves in the fall and are bare during the winter. Evergreens never drop all of their leaves. A conifer is a type of evergreen plant. All conifers are evergreen, but not all evergreens are conifers. But the definition of conifer is:

con·i·fer (kn-fr, kn-)

n.

Any of various mostly needle-leaved or scale-leaved, chiefly evergreen, cone-bearing gymnospermous trees or shrubs such as pines, spruces, and firs.

Cedars, or very similar plants called Junipers, are "scale-leaved" as listed in the definition above. So, Cedars are conifer evergreens, as opposed to most Holly plants, for example, which are broad leaf evergreens.

A cedar is a conifer and it is evergreen. Not all conifers are evergreen i.e. the larch.