Noun ob has 2 senses

• ob(n = noun.object) ob river - a major river of western Siberia; flows generally northward and westward to the Gulf of Ob and the Kara Sea; Array
is a part of siberia
is a kind of river

• ob(n = noun.cognition) midwifery, obstetrics, tocology - the branch of medicine dealing with childbirth and care of the mother; Array
is a kind of medical specialty, medicine
has particulars: fetology, foetology, perinatology