Involved in the biosynthesis of ent-kaurene diterpenoids natural products such as oridonin, miltiradiene, eriocalyxin B and nezukol, known to exhibit antitumor, anti-inflammatory and antibacterial activities, and in the production of gibberellins phytohormones (PubMed:30496917). Catalyzes the conversion of (2E,6E,10E)-geranylgeranyl diphosphate (GGPP) to ent-copalyl diphosphate (ent-CPP) (PubMed:30496917). (2E,6E,10E)-geranylgeranyl diphosphate = ent-copalyl diphosphate Plant hormone biosynthesis; gibberellin biosynthesis. Secondary metabolite biosynthesis; terpenoid biosynthesis. Accumulates in leaves, and, at low levels, in germinating seeds. Moslty expressed in leaves where ent-kaurane diterpenoids accumulates but weakly expressed in germinating seeds in which gibberellins are produced. The Asp-Xaa-Asp-Asp (DXDD) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family. Tpsc subfamily.