Q. I well remember " . . . and sometimes 'y'" as part of the group of vowels in English. But how can I tell whether the letter "y" is being used as a consonant or a vowel?

A. The letter "Y" is being used as a vowel in words such as eye and apply, where it provides the same kind of sound that the letter "I" would have in the same situation. When "Y" is used as a consonant it has the sound at the beginning of words like yes, yak, young, or yawn.

Q. The etymology of volteface, or "about-face," states that the word's ultimate origin is the Italian word voltafaccia, from voltare. But volta is the past participle of volgere in Italian, not of voltare.

A. Voltafaccia is an example of a common type of Western Romance language compound in which a verb in the third person singular present indicative is followed by a direct object; the past participle of volgere would not be appropriate in this case.

Other words that follow this pattern include parasol and parapet. These are compounds in which the Italian subject word itself is deleted: "(he/she/it) turns face," "(it) blocks (the) sun," "(it) shields (the) breast," etc.

Such compounds are common in French as well: abat-jour ("lampshade") and gratte-ciel ("skyscraper"). Notice that the English versions of these last examples follow a "noun + verb" model. English has words like turncoat, pickpocket, and scarecrow, but overall this is not a very productive type of word-formation for English speakers.

Q. The Tenth Collegiate gives this example under the word historic: "an historic occasion." The online dictionary now says "a historic." Why and when did the article change?

A. Either a or an before the word historic is correct. Here's a discussion of the question from Merriam-Webster's Dictionary of English Usage:

Before h in an unstressed or weakly stressed syllable, a and an are both used in writing ("an historic," "a historic") but an is more usual in speech, whether the h is pronounced or not. This variation is the result of historical development: in unstressed and weakly stressed syllables, h was formerly not pronounced in many words where it is pronounced at the present time. A few words, such as historic and (especially in England) hotel, are in transition, and may be found with either a or an. You choose the article that suits your own pronunciation.