All, I am wondering how the same word may refer to two opposite meanings. According to the free dictionary https://www.thefreedictionary.com/overlooked, overlooked may mean a thorough examination or to fail to observe. For me, those seem to be opposite meanings. thanks
This is a case where meaning is not separate from its context (it rarely is). A word may have several dictionary definitions but sometimes we can only decide on the correct one by looking at the context. For example, "I saw wood" is ambiguous, whereas "I saw wood with my eyes" or "I saw wood with a sharp tool" both make the meaning of "saw" clear.
There are others examples similar to your question about overlooked. Here are two examples of such antonymic homonyms:
= to divide by or as if by a cutting blow : SPLIT “The blow cleaved the victim's skull.”
= to adhere firmly and closely or loyally and unwaveringly
= to give effective or authoritative approval or consent to
= to impose a sanction or penalty upon