Here are the common Latin words used in English language.

Impromptu

It means spontaneous or without preparation.
Something that catches you by surprise: “my boss
called an impromptu meeting today and my
colleagues and I were totally unprepared.”
Quid pro Quo

It means “of equal exchange or substitution.”
Literally, it means “something for something”. You
exchange something of the other’s interest for
something of your own interest. “They finally agreed
on a quid pro quo agreement, in which John will
disclose confidential information to George in
exchange for free access to George’s company
database.”
Per se

In itself, intrinsically, of an inherent nature. “My
friends and I were celebrating and having a great
time, but it really wasn’t a party per se.”
A Priori

Based on hypothesis or theory, rather than
experience. Derived by logic, with no observed facts.
“Although I have never been a bachelor myself, I of
course know a priori that all bachelors are
unmarried.”
Ad hoc

For one specific case, many times can be replace by
“specific”. “We did not have an HR manager at the
company, so I formed an ad hoc HR committee.”
Bona Fide

Unquestionable, in good faith. “Since my boss has
never been friendly to me, I was surprised when he
offered me his bona fide advice on how I could
succeed in business.”
Pro Rata

Proportionally, in equal parts. “Many people like to
split the check pro rata so that they can order more
than they would if paying the full price.”
Ergo

Therefore, consequently. “I have never been to Kim’s
apartment. Ergo, I cannot tell you what it looks like.”