I thought this would be fun and informative, the word derivation for common military ranks! I have taken all of this information from the Oxford English Dictionary, the last word in... uh... words.
Colonel - ORIGIN mid 16th cent.: from obsolete French coronel (earlier form of colonel), from Italian colonnello ‘column of soldiers’, from colonna ‘column’, from Latin columna. The form coronel, source of the modern pronunciation, was usual until the mid 17th cent.
Lieutenant (which, despite what our British friends think, does not contain the word "left") - ORIGIN late Middle English: from Old French (see lieu, tenant). Note: as in someone who Tenant (holds) in lieu.
General - ORIGIN Middle English: via Old French from Latin generalis, from genus, gener- ‘class, race, kind’. The noun primarily denotes a person having overall authority: the sense ‘army commander’ is an abbreviation of captain general, from French capitaine général ‘commander-in-chief’.
Admiral - ORIGIN Middle English (denoting an emir or Saracen commander): from Old French amiral, admirail, via medieval Latin from Arabic 'amr ‘commander’ (from 'amara ‘to command’). The ending -al was from Arabic -al- ‘of the’, used in titles (e.g. 'amr-al-'umar ‘ruler of rulers’), later assimilated to the familiar Latinate suffix -al. (Comes from Emir, neat)
Captain - ORIGIN late Middle English (in the general sense ‘chief or leader’): from Old French capitain (superseding earlier chevetaigne ‘chieftain’), from late Latin capitaneus ‘chief’, from Latin caput, capit- ‘head’.
Private - ORIGIN late Middle English (originally denoting a person not acting in an official capacity): from Latin privatus ‘withdrawn from public life’, a use of the past participle of privare ‘bereave, deprive’, from privus ‘single, individual’.
Ensign - ORIGIN late Middle English: from Old French enseigne, from Latin insignia ‘signs of office’ (see insignia).
Sergeant - ORIGIN Middle English: from Old French sergent, from Latin servient- ‘serving’, from the verb servire. Early use was as a general term meaning ‘attendant, servant’ and ‘common soldier’; the term was later applied to specific official roles.
Interesting seeing where these words come from! Hope you enjoy!
"Neca eos omnes. Deus suos agnoscet!"
(Kill them all. God will know his own.)
-- Arnaud-Armaury, the Albigensian Crusade