This word has an almost identical connotation but seems to have shifted in meaning in modern American usage towards almost requiring that the thing/person in question is named after whatever/whoever is mentioned.
Namesake is a term used to characterize a person, place, thing, quality, action, state, or idea that has the same, or a similar, name to another - especially (but not exclusively) if the person or thing is actually named after, rather than merely sharing the name of another.
For example, if a person, place, or thing has the same name as another - especially if they are named after another person, place, or thing, then the name target is said to be the namesake of the name source. The earliest use reported in the Oxford English Dictionary was in 1635. Dictionaries suggest that the word probably comes from "name's sake", "for one's name('s) sake", for "name sake".
There has been some discrepancy as to whether the name source or the name target takes the term namesake. According to the American Heritage Dictionary, a namesake is a person or thing named after another. In other words, the name target takes the term namesake, as in
"I was named after my grandfather. I am his namesake."
"Julian's Castle, Julian's namesake restaurant."
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. Merriam-Webster's Dictionary defines "namesake" as "one that has the same name as another; especially one who is named after another or for whom another is named", allowing the usage of:
"I met a person who happened to have the same name as me. We are namesakes."
By "for whom another is named", Merriam-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 eponym or "namegiver", which refers to the name source as providing the name to the name receiver.