Namesake (sometimes "name's sake") is a term used to characterize a person, place, thing, quality, action, state, or idea that is called after, or named out of regard to, another. For example, if a target person, place, or thing is named after a source person, place, or thing, then the name target is said to be the namesake of the name source. First recorded in 1646 to mean "person named for the sake of someone", the reference to something being a namesake of something else imports a connection between the two that extends beyond sharing similarly looking names to one of a shared name, usually called the same name. Namesake may be distinguished from eponym in that a namesake usually includes a "sake" connection to the source name whereas an eponym name merely is derived from a source name without an additional sake connection.
Some commercial entities and products are named after their creators, such as the Trump Tower and Ford Motor Company. Items are also named after people associated with them, such as the teddy bear. This is especially the case with scientific discoveries and theories, such as Gibbs free energy. When the target name merely is derived from the source name without an additional "sake" connection, such usage more accurately may be called an eponym rather than a namesake.
"I was named after my grandfather. I am his namesake."
The Oxford English Dictionary and Merriam-Webster's Collegiate Dictionary are not so restrictive. According to the Oxford English Dictionary, a namesake is a person or thing having the same name as another. Webster's Dictionary defines "namesake" as "one that has the same name as another; esp. one who is named after another or for whom another is named." By "for whom another is named", Webster's Dictionary allows the term namesake to be used in reference to the name source as in,
"I was named after my grandfather. He is my namesake."Both usages of namesake are correct. This ambiguity sometimes may be resolved by the term namegiver, which refers to the name source as providing the name to the name receiver.