Idiomatic Expressions — English Bac STM

Dans le programme du Bac STM

English carries a coefficient of 2 in the Bac Sciences et Technologies Mécaniques (STM) stream. The core subjects are Mathematics and Engineering Sciences (coefficient 7 each), then Physics-Chemistry (coefficient 5). English and Philosophy (coefficient 2) form the margin where candidate rankings and honours are settled. Mastering the structure of a piece of writing matters more here than memorising it.

À l'épreuve

Three parts: Reading Comprehension, Language, and Writing (about 180 words). Reading technical drawings and function diagrams builds the same skill an essay needs: breaking an argument into parts and rebuilding it as a coherent plan.

Objectifs d'apprentissage

Reuse this vocabulary field in the Bac STM Reading answers and in the argumentative essay (coefficient 2)
Understand that an idiom's meaning is figurative and not deducible from its words
Recognise frequent programme idioms: once in a blue moon, break the ice, a piece of cake, under the weather, cost an arm and a leg
Paraphrase an idiom in plain English when its meaning is not certain
Avoid translating an idiom word for word from Arabic or French

Notions clés

What is an idiom?

A fixed group of words whose overall meaning is figurative and different from the literal sense of its parts. E.g. “to break the ice” = to ease the tension at the start of a conversation, nothing to do with real ice.

Frequent programme idioms

once in a blue moon (very rarely), break the ice (ease initial tension), a piece of cake (very easy), under the weather (slightly unwell), cost an arm and a leg (be very expensive), let the cat out of the bag (reveal a secret).

Paraphrasing an idiom

If you are unsure of an idiom in an exam, replace it with a plain paraphrase: “extremely expensive” for cost an arm and a leg, “very easy” for a piece of cake. A correct paraphrase scores; a wrong literal translation does not.

Collocations and word associations

A collocation is a pair or group of words that native speakers naturally use together: you make a decision but do your homework, you take a photo, pay attention, catch a cold. Common patterns: verb + noun (raise awareness, bridge the gap, meet a need), adjective + noun (heavy rain, strong coffee, sustainable development), adverb + adjective (highly qualified, deeply concerned). In the vocabulary section, a gap such as « The government should … awareness of pollution » expects raise, not make or do. Learn new words with their partners, not alone, and group them by theme (education, environment, technology) to reuse them in writing.

Erreurs fréquentes

Translating an idiom word for word: “il pleut des cordes” → “it's raining ropes” is meaningless in English; the equivalent idiom is “it's raining cats and dogs”.

Taking an idiom literally in a reading text: “he was over the moon” means he was delighted, not that he was in space.

Overusing idioms in a formal essay: one or two well-placed idioms add colour, but a formal argument is not built on them.

Exemple corrigé

Énoncé

Explain the meaning of the idiom in this sentence and rewrite it in plain English: “The new laptop cost me an arm and a leg.”

Correction

Identify the idiom. “cost an arm and a leg” is a fixed idiom, not a literal statement.

Give the figurative meaning. It means “to be very expensive”.

Rewrite in plain English. “The new laptop was extremely expensive.”

Le cours, puis l'entraînement.

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3 exercices pour t'entraîner

Exercice 1

Easy

What does “a piece of cake” mean? (a dessert / something very easy / a small portion)

Voir la correction

something very easy — “The test was a piece of cake” = the test was very easy.

Exercice 2

Medium

Replace the idiom with a plain paraphrase: “I only see my cousins once in a blue moon.”

Voir la correction

“I only see my cousins very rarely.” — once in a blue moon means very rarely.

Exercice 3

Hard

A student writes “I feel under the weather today, so I will not go to space.” Explain the mistake and correct the sentence.

Voir la correction

The student has taken “under the weather” literally. It is an idiom meaning “slightly unwell”. Corrected: “I feel under the weather today, so I will stay at home.”

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Questions fréquentes

How many idioms do I need for the Bac?

A working set of ten to fifteen frequent ones is enough. Knowing their meaning matters more for reading; in writing, one or two well-chosen idioms are plenty.

Can I use a French or Arabic idiom translated into English?

No — idioms rarely translate. Either use the established English equivalent or drop the idiom and state the meaning plainly.

How do I handle an unknown idiom in a reading text?

Use the surrounding context: the sentence and paragraph usually make the figurative meaning clear enough to answer the question, even without knowing the idiom.

English is far from my mechanical specialism — how do I approach it?

Treat it as a system with inputs and outputs: the input is a prompt, the processing is analysis then discussion, the output is a conclusion that settles the question. Learn that flow, apply it to the 31 chapters with two examples each, and one weekly session is enough to raise the mark.

How do I use this theme in the Bac STM essay without sounding generic?

Anchor each key term in one concrete, personal example — a place, a person, a situation you know. A specific illustration in accurate English scores better than a long list of terms with no support, on any of the society prompts in the programme.