(literary) they

combination, fusion, merger / blending, harmonization

to be or become combined, fused, merged / to be or become blended, harmonized

perfect, completed

completeness / perfection

idea, invention

(physics) short for 原子核融合 (genshikaku yūgō): (atomic) nuclear fusion / (biology) karyogamy, the fusion of cellular nuclei when a sperm cell meets an egg cell

those (referring to things distant from the speaker)

perfectionism

(computing theory) Turing complete