Пост: fast, post
This week begins the seven-week fast — Великий Пост (Lent) — that precedes the great celebration of Пасха (Easter). For pious Orthodox Christians, this is a time of abstinence, prayer and good works. But to the contrary, for vegans and vegetarians, it is a time of joyful gluttony. For a few weeks every restaurant and cafe has a постное меню (fasting menu), and even the smallest supermarket stocks соевый сыр (tofu, literally "soy cheese"), миндальное молоко (almond milk) и постный майонез (non-dairy mayonnaise). Folks with lactose intolerance — rejoice!
Пост is one of those interesting words that has been imported into the Russian language three times with three different meanings. The oldest and most obscure borrowing is of пост as a fast.
Etymologists argue in their polite way about when and where this took place, and when they cite Moravian-Pannonian Slavic tribes, my eyes begin to glaze over. Whenever and however and from whomever it was borrowed, by the 11th century пост was used in religious texts.
If you want to say you are fasting, you can use the verb поститься, which usually, but not always refers to a religious fast: Недаром же люди постятся во время серьёзной творческой работы (There's a good reason why people fast during serious creative work). Or you can say держать or соблюдать пост (to hold to or observe the fast).
Of course, fasting is not easy, especially considering it means abstinence from meat, dairy, most alcohol, frivolous entertainment like television, movies, murder mysteries and even sex. Я старался, но всё-таки нарушал пост (I tried, but I broke the fast anyway).
If you are talking about fasting, it's good to know the adjectives постный (what you can eat or drink on a fast) and скоромный (what you can't eat or drink, from a word that originally referred to animal fat).
In very rarified contexts, скоромный can also have the figurative meaning of something vulgar and distasteful.
Ребята пришли и отпускали разные скоромные шуточки, пока моя мама их не выгнала. (The guys came over and made a bunch of vulgar jokes until my mother threw them out.)
The second borrowing of пост came from the Latin via French and Italian. This пост refers to the three post p's: place, people and position. That is, пост can be a place of observation, like пост ГАИ (auto inspectorate post) or пост медсестёр (the nurses' station). Стоять на посту means to be on guard duty. Or пост can mean the people doing the observing or guarding, like сторожевой пост (guards) or санитарный пост (medics).
Or it can be a position in a company, government or military, usually high up: Путин понимал, что люди из его ближнего круга далеко не готовы занять ключевые посты в государстве. (Putin realized that men in his intimate circle were hardly willing to hold key government positions.)
And the third borrowing is from English social networks — пост as in what you post on your Facebook page. You might be directed to лучшие посты на эту тему (the best posts on this topic), or asked to do репост (repost) or перепост (repost), sometimes with the verbs постить (to post) and перепостить (to repost): Просьба максимально перепостить! (Please repost as much as possible!)
All of these posts give us simple souls plenty of fun: Я перепостила, что он согласился на новый пост во время Великого Поста (I reposted that he agreed to take the new position during Lent).