Learn English – Latin-derived terms for directions

The trailing i on most masculine nominative plurals in Latin is usually a “long e” /iː/, as has already been stated, like ee in levee or tree. Latin pueri (the boys) would be /pu.eri/ poo-air-ee.

A trailing ae like that found on most feminine nominative plurals is a diphthong which sounds a lot like a “long i” (/aɪ/, [äɪ̯]), but, as it is a diphthong, is more of a switch in sound starting with a “short a” /ɑ/ and ending with a “long e” /iː/, similar to the pronunciation of aye or eye /aɪ/. Thus, Latin puellae (the girls) would be poo-ell-aye /puɛlːaɪ/.

I’s at the beginning of words are pronounced like the y /j/ in yet /jɛt/ or yellow /ˈjɛloʊ/, and C’s were usually hard /k/. So, Julius Caesar (which would have been written ‹Iulius Caesar›, as they didn’t have J’s), would have been pronounced something like Yul-ee-us Kai-sar /ˈjuː.li.ʊs ˈkae̯.sar/, the pronunciation of which is where Germans get the word Kaiser, Russians get Czar, and Arabs get Qaysar, amongst a dozen other languages that have words rooted in the word Caesar.

In the past, to be left-handed was considered touched by the Devil. As Wikipedia notes:

Historically, the left side, and subsequently left-handedness, was considered negative in many cultures. The Latin word sinistra originally meant "left" but took on meanings of "evil" or "unlucky" by the Classical Latin era, and this double meaning survives in European derivatives of Latin, and in the English word "sinister".

Meanings gradually developed from use of these terms in the ancient languages. In many modern European languages, including English, the word for the direction "right" also means "correct" or "proper", and also stands for authority and justice. In most Slavic languages the root prav is used in words carrying meanings of correctness or justice.

So, if you were left-handed or sinister, you were associated with evil. In time, sinister itself meant evil and threatening. EtymOnline said that sinister attained this meaning in the early 15th century. The OED supports this, writing that the first uses of sinister to mean malicious were:

1474 Rolls of Parl. VI. 110/1 Contynuyn in habundaunce of goodes and havour, to their sinister pleasure.

1477 Earl Rivers tr. Dictes or Sayengis Philosophhres (Caxton) (1877) lf. 7, Leste ye be let or withdrawen ther fro by eny sinistre or euil temptacion.