capital (adj.) Look up capital at Dictionary.com
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" (see capitulum).

Meaning "principal" is early 15c. Of letters, "upper case," from late 14c. A capital crime (1520s) is one that affects the life or "head;" capital had a sense of "deadly, mortal" from late 14c. in English, a sense also found 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.

Capital gain is recorded from 1921. Capital goods is recorded from 1899. Of ships, "first-rate, of the line," attested from 1650s. Related: Capitally.
capital (n.1) Look up capital at Dictionary.com
early 15c., "a capital letter," from capital (adj.). The meaning "capital city" is first recorded 1660s (the Old English word was heafodstol). The financial sense is from 1610s (Middle English had chief money "principal fund," mid-14c.), from Medieval Latin capitale "stock, property," noun use of neuter of capitalis "capital, chief, first." (The noun use of this adjective in classical Latin was for "a capital crime.")
[The term capital] made its first appearance in medieval Latin as an adjective capitalis (from caput, head) modifying the word pars, to designate the principal sum of a money loan. The principal part of a loan was contrasted with the "usury"--later called interest--the payment made to the lender in addition to the return of the sum lent. This usage, unknown to classical Latin, had become common by the thirteenth century and possibly had begun as early as 1100 A.D., in the first chartered towns of Europe. [Frank A. Fetter, "Reformulation of the Concepts of Capital and Income in Economics and Accounting," 1937, in "Capital, Interest, & Rent," 1977]
Also see cattle, and compare sense development of fee, pecuniary.
capital (n.2) Look up capital at Dictionary.com
"head of a column or pillar," late 13c., from Anglo-French capitel, Old French chapitel, or directly from Latin capitellum "little head," diminutive of caput (see capitulum).