Cognates Within The Same Language
Cognate doublets can exist within the same language, with meanings which may be anything from slightly to totally different. For example, English ward and guard (*wer-, "to perceive, watch out for") are cognates, as are shirt (garment on top) and skirt (garment on bottom) (*sker-, "to cut"). In some cases, such as "shirt" and "skirt", one of the cognate pairs has an ultimate source in another language related to English, while the other one is native, as happened with many loanwords from Old Norse borrowed during the Danelaw. Sometimes, both cognates come from other languages, often the same one but at different times. For example, the word chief (meaning the leader of any group) comes from the Middle French chef ("head"), and its modern pronunciation preserves the Middle French consonant sound; the word chef (the leader of the cooks) was borrowed from the same source centuries later, by which time the consonant had changed to a "sh"-sound in French. Such word sets can also be called etymological twins, and of course they may come in groups of higher numbers, as with, for example, the words wain (native) wagon (Dutch) and vehicle (Latin) in English.
An example of very different and non-obvious English-language cognates is grammar and glamour.