Quote Originally Posted by bobert View Post
To say "She chopped an onion" would it be:

Она нарубленный лук.
One other comment for bobert: The sentence you've got here could be translated back to English as "She is a chopped onion." In other words, you've used a past passive participle ("that which has been chopped", нарубленный) instead of a simple past-tense active verb ("she has chopped", нарубила). Since textbooks for foreigners learning Russian normally teach you how to form the basic past tenses LONG before dealing with past passive participles, it makes me suspect that you copied-and-pasted the participial form нарубленный from Google Translate.

I'm not saying this to make fun of you, bobert -- it's just that using automatic translation software is a really bad habit for a beginning language learner and will end up causing you unnecessary confusion with Russian grammar, because the software itself gets confused.

I just went to Google Translate and entered a few example sentences like "She chopped the onion", "She was cutting the onion," "She has cut the onion," "She chops the onion", etc., to see how they'd be translated на русский. The present-tense constructions came out more or less okay, but the software "choked" on most of the past-tense English forms and produced Russian sentences that meant "She is a chopped onion" or "She is pruning back the onion plant," and so forth.

It's okay to use Google Translate for individual words, but it's really best to avoid it when dealing with phrases and complete sentences (until you're farther along in your Russian studies and know the grammar well enough that you can instantly spot when Google Translate has "choked" on a phrase).
Since onions are uncountable, must глава be used to indicate that only a single onion is being chopped?
Others have already mentioned the word луковица ("a single onion bulb") -- but it might also be useful for you to know the generic term штука ("a single unit/item of something") when dealing with Russian "mass nouns" like onions, potatoes, carrots, strawberries, and other produce. So in written recipes, the phrase "лук -- две штуки" ("onion -- two units") can mean the same thing as "две луковицы" ("two onion-bulbs"). It's a handy work-around if you can't remember the countable forms.