Pupil = A person who is taught by another, esp. a school child or student in relation to a teacher.

• All pupils are expected to attend school assembly.
• A primary school pupil

Student  = 1) A school pupil 

• A highschool student

2) A person who is studying at a University or other places of higher education.

• A student of MBA course.
• A group of college students.

The difference: All the PUPILS are STUDENTS but all the STUDENTS are not PUPILS. Pupils are more dependent on teachers and the teachers teach them.

But in graduate or post-graduate level, the students are NOT called pupils. They are more independent and college faculty share their knowledge with the students and in other words students are learners. And when it comes to the post-graduate level, they are more or less like participants of a workshop and teacher(professor) will be playing the role of a team-head and the students are learners or participants.

Incidentally, note the following difference:

• Boys’ or girls’ school.
• But, Men’s or women’s college.

Lunch = meal taken in the middle of the day.

Supper = meal taken in the evening/night.

Dinner = the main meal of the day eaten either at mid-day or in the evening.

DINNER doesn’t necessarily mean a meal eaten at the evening or night. According to English customs, there is only one main meal a day (either at midday or in the evening) and they call it DINNER.

When you have your main meal in the midday, you call it dinner instead of lunch, and evening meal being supper.

Similarly, when you have your main meal in the evening, you call it dinner and the midday meal will be called lunch. (Not dinner)

RECAP:

Breakfast – Lunch – Dinner (Not supper)

Breakfast – Dinner – Supper (Not Dinner)

Examples:

• The children have to pay for their school dinners. (i.e., midday meal provided by the school)
• What time do you have your dinner?

However: Dinner is a formal occasion/party in the EVENING when this meal is eaten.

• I’ve received an invitation to dinner.
• We are giving a dinner in honour of our retiring Executive Director, Jorty.

Similarly: If a formal party is held at midday with a meal, we call it LUNCHEON.

I) English (noun) = The English language.

(adjective) Relating to England, or its people or language.

• English customs demand such polished manners.

II) The English = English people, the people of England.

• The English are among the world’s most cosmopolitan and well-travelled people.

III) Speak English – i.e., you know and can speak English.

• Do you speak English?
• My parents do not speak English.

IV) Speak in English = use English on a particular occasion.

• When I went to Chennai I had to speak in English as I didn’t know Tamil well.
• When the tourists came to Kovalam the guide spoke to them in English.

Upstairs and downstairs are not used with to/in/at etc. They are mainly adverbs, but they are also used as adjectives and nouns.

As adverb:

• He went upstairs to answer the phone. (NOT to upstairs)
• The people who live upstairs are very noisy.

As adjective:

• My room is upstairs (NOT in upstairs)
• The dining room and kitchen are upstairs. (NOT in upstairs)
• The upstair(s) rooms. (often without the final ‘s’)

As noun:

• She’s cleaning the upstairs.
• The upstairs of this house is for sale.

The above rules are equally applicable to ‘downstairs’ also.

Is there a word like Equipments?

The answer is an emphatic NO.

For the word equipment, there is no plural. It is an uncountable noun.

More uncountable nouns:

• Information, etiquette, jewellery, food, news, toast, scenery, nonsense, jargon, porcelain, cutlery, crockery, earthenware, luggage, baggage, etc.