monosubstitution
/ˌmɒnə(ʊ)sʌbstɪˈtjuːʃn/ /ˌmɒnə(ʊ)sʌbstɪˈtʃuːʃn/Chemistry
noun
Substitution affecting only one of the atoms or positions in a molecular structure.
Origin
Late 19th century; earliest use found in Henry Watts (1815–1884), chemist. From mono- + substitution.