Capitol (n.)

early 13c., "of or pertaining to the head," from Old French capital, from Latin capitalis "of the head," hence "capital, chief, first," from caput (genitive capitis) "head" (from PIE root *kaput- "head"). The meaning "main, principal, chief, dominant, first in importance" is from early 15c. in English. The modern informal sense of "excellent, first-rate" is by 1754 (as an exclamation of approval, OED's first example is 1875), perhaps from earlier use of the word in reference to ships, "first-rate, powerful enough to be in the line of battle," attested from 1650s, fallen into disuse after 1918. Related: Capitally.

A capital letter "upper-case latter," of larger face and differing more or less in form (late 14c.) is so called because it stands at the "head" of a sentence or word. Capital gain is recorded from 1921. Capital goods is recorded from 1899.

A capital crime or offense (1520s) is one that involves the penalty of death and thus affects the life or "head" (capital had a sense of "deadly, mortal" from late 14c. in English, as it did earlier in Latin). The felt connection between "head" and "life, mortality" also existed in Old English: as in heafodgilt "deadly sin, capital offense," heafdes þolian "to forfeit life." Capital punishment was in Blackstone (1765) and classical Latin capitis poena.