In English, chef, chief, captain and head all mean the same thing: leader. (Though chef and captain are often leaders of specifically kitchen or ship/squadron specifically.) The four words have four different initial sounds (sh, ch, k, h) and mostly different first vowel and second consonant, and yet they are all cognates! The differing sounds are a result of phonetic changes.
Words undergo semantic change as well as phonetic change. It is very common for the word for "head of an animal's body" to be adapted to mean "head of a group, leader, or principal." English head still retains "head of an animal's body" as its primary meaning. As with most body parts, this latter meaning tends to be preserved, but there is a substitution seen in some languages. A word for "bowl or jug" sometimes comes to mean "human head" by a slangy analogy. In German, "Kopf" (head) derives ultimately from a word for cup. In French the word tête has undergone both transitions! It started as a word for manufactured cup, came to mean head of body, and is now also used to mean head of a group.
Let's mention six specific ancient words in the Proto-Indo-European language that are relevant to our discussion: Each of these six words ultimately changed into a word with one or both of the two meanings of head.
(1) Several English words derive from PIE ker. "Corn" (hardened skin, often on the foot) came to English via Latin cornu and Old French corne. "Cranium" came from Greek kranion (skull). "Horn" itself is cognate with its PIE synonym, coming from Germanic hurnaz, the sound change k>h being a regular feature of Germanic. Several other English words derive from this PIE root, e.g. "cerebral" (which comes from French where k>s is a regular sound change; and perhaps even words like "democracy" which derive from Greek kratos (strength) which may have come from the analogous meaning (hard) of PIE ker.
(2) English "load" (the cargo on a course or road) derives from proto-Germanic laitho (course or road) which derives from PIE leit (to go forth). English "lead" or "leader" derive from proto-Germanic laidjan (to travel) which also derives from PIE leit (to go forth).
(3) English "hive" derives from PIE keup via Germanic hufiz (hull). English "coop" and "cup" each derive ultimately from Latin cupa (tub, cask) (or its Late Latin form cuppa) although they were borrowed from Latin independently. That Latin root also traces to PIE keup. Middle German "Kopf" (bowl) may also derive from cuppa, and has since been adapted to be the Modern German word for head. (There was no k>h sound change since this was a borrowing from Latin after the sound change ocurred in Germanic.)
(4) I mention PIE teks (to weave) because it was the versatile PIE word which came to refer to various woven or manufactured goods, including bowl; it is the original source of French tête. It is also the ultimate source of several English words, most obviously "textile" but also "text" and "technology."
(5) PIE skel (to cleave) became Germanic skaljo (shell, husk) the source of several English words including "skull."
(6) Finally we consider PIE kaput (head of body). (There is a slang "kaput" in English, borrowed from German, but its relation to the ancient PIE word is very indirect.) Because of the k>h sound change, kaput became haubudam in Germanic, then heafod in Old English and "head" in Modern English, as well as Modern German Haupt (head, both meanings). Latin's caput derived from the PIE root and already had both meanings of "head." The Old French words chief and capitaine both derived from a form of the Latin word, but the latter was borrowed after the k>ch sound change, and therefore retains Latin's k sound. English "chief" and "captain" were borrowed from the Old French words. English "chef" is a re-borrowing of the Middle French form of "chief" but was borrowed after French's ch>sh sound change.
There are many other English words that derive ultimately from PIE caput, including "achieve," "biceps," "cabbage," "cadet," "cap," "cape," "capital," "corporal," "occipital."
So English "head," "captain," "chief," and "chef" are not only synonyms but are cognates!
English "five" and Spanish "cinco" are also cognates.
Diachronic Linguistics is fun!