NEW YORK  (Reuters) - "Quomodo dicis latine life-jacket?" quipped one of the Latin-speaking passengers on a tour boat circumnavigating Manhattan on a rainy Sunday morning in May, just after the captain's safety announcement. "How do you say life-jacket in Latin?"

Luckily, one of the greatest living experts in spoken Latin was on hand with the answer, instantly recalling the word used by the Roman poet Horace in his "Satires" about 2,000 years ago.

"Horace says, 'When you grow up, nabis sine cortice' - you will swim without a float, or a life-jacket," said Father Reginald Foster, a Carmelite monk and priest.

Foster spent most of his working life translating the Pope's words into Latin at the Vatican and teaching spoken Latin to Catholic scholars, Latin teachers, graduate students and anybody else who was interested.

Now retired from the Vatican and living in a monastery in his hometown of Milwaukee, Foster is something of a celebrity in the rarefied world of Latin scholarship. His visit to New York last weekend, at the invitation of a foundation created to continue his teaching work, drew former students (including this reporter) from as far as Maine and Virginia.

On the agenda: seminars on teaching Latin as well as Latin-themed excursions such as a tour of the New York Botanical Gardens with Latin commentary and a visit to the site of George Washington's crossing of the Delaware to read "Life of George Washington in Latin Prose," by Francis Glass, published in 1835.

On the boat trip, the text was a description of the island of Manhattan published in Latin in 1633 by the Dutch explorer Johannes de Laet. The writer remarked on the weather (much like what he was used to), the richness of the soil (good for producing wine and cannabis) and the savagery of the original inhabitants (no religion or politics).

The Paideia Institute (http://paideia-institute.org/), which organized the visit, is dedicated to promoting the study of Latin at a time when fewer American children are learning any foreign languages.

According to the American Classical League, Latin enrollment is not declining as fast as other languages and it is even expanding at the elementary school level, largely due to the expansion of charter schools.

Paideia runs a Latin summer school in Rome modeled on a program Foster ran for years. Students read original texts in the locations they were written, from Cicero's speeches in the Roman forum to Pliny's description of the eruption of Vesuvius at Pompeii, which was destroyed by the volcano in 79 AD.

Since the focus is on living Latin, they are also pushed to speak the language.

"The first couple of days, it was pretty quiet," admits Christopher Cochran, 20, a junior at Princeton who attended Paideia's first session in Rome in 2011.

Foster, who is in his 70s and uses a wheelchair, still teaches. He also is working on a series of books, "Corpus Latinitatis," compiling the teaching materials he developed over several decades. (www.thelatinlanguage.org) The first installment, titled "Ossa Latinitatis Sola," or "The mere bones of Latin," is now with the publisher, Catholic University of America Press, which has yet to set a date for publication.

Foster laments that for many people, learning Latin will forever be associated with rote-learning declensions and conjugations. Teachers who impose that "are committing crimes against humanity," he said in a speech to Latin teachers explaining his methods a few hours after the boat tour.

He has always incorporated every kind of Latin in his teaching, from Roman poets to the liturgy, from St. Augustine to Papal encyclicals he translated himself.

"We start more or less with Plautus, around 184 BC," he said. "And we go up until tweets that we wrote yesterday for the Pope in Latin that are going around the world tomorrow."

The Pope's Latin tweets, penned with a little help from Foster who is in regular touch with his successor at the Vatican, can be found at @Pontifex_ln.

(Editing by Patricia Reaney and Doina Chiacu)