In formal writing, certain adjectives are the partners writers reach for first with certain nouns, to signal how serious something is. Each has a small family of nouns rather than just one (dire warning, profound change, grave error are all standard). All three below belong to a serious, formal register. Dire consequences are outcomes that are extremely severe and hard to undo. A profound effect is an influence that reaches deep and lasts, and impact takes the same partner, so a profound impact is just as standard. Grave concern means serious, weighty worry about a threat, worry strong enough that people feel something must be done. Swapping in a generic word like 'bad' or 'strong' still makes sense, but it drains the seriousness out and sounds flat.
Adjectives that raise the stakes
dire consequences /ˈdaɪr ˈkɑnsəkwɛnsəz/ — Ignoring the safety warnings could have dire consequences for the whole team.
profound effect /prəˈfaʊnd ɪˈfɛkt/ — The new teacher had a profound effect on how the students saw themselves.
grave concern /ɡreɪv kənˈsɜrn/ — The falling water levels are a source of grave concern to local farmers.
Not ""Ignoring climate change will have bad consequences." ('bad' is understood but weak and flat in formal writing)" — say ""Ignoring climate change will have dire consequences." (the fixed formal collocation)". Dire is the partner that carries real weight with consequences. 'Bad consequences' isn't wrong, but it drains the seriousness out of a formal sentence.
Try it: The teacher changed how the students saw themselves, and they still feel it years later. Which phrase names an effect that reaches deep and lasts? (a profound effect / a wide effect / a heavy effect) Answer: a profound effect — 'Profound' is the partner formal writing reaches for when an effect goes deep and lasts, which is what 'still feel it years later' describes. 'Wide effect' would be about how many people it reached, and 'heavy effect' isn't a natural pairing with 'effect' at all.
Adjectives that show scope
Other collocations tell you how wide or how large something reaches. An overwhelming majority is a very large, decisive one, so big that the other side barely counts. Widespread concern is worry shared across many people or places, not just a few. A heated debate is an intense, emotional argument where feelings run high. These are the partners formal English prefers, so a casual swap like 'big majority' or 'hot debate' still makes sense but sounds flatter than a report wants.
overwhelming majority /ˌoʊvərˈwɛlmɪŋ məˈdʒɔrəti/ — An overwhelming majority of members voted to keep the library open.
widespread concern /ˈwaɪdˌsprɛd kənˈsɜrn/ — There is widespread concern about the rising cost of housing in the city.
heated debate /ˈhitəd dɪˈbeɪt/ — The proposal to shorten the school year sparked a heated debate among parents.
Not ""A big majority of the council backed the plan." ('big' is understood but too casual for a formal report)" — say ""An overwhelming majority of the council backed the plan." (the fixed collocation for a large, decisive vote)". Overwhelming is the partner that signals a decisive scale with majority. 'Big majority' isn't wrong, but it sounds informal where a report needs weight.
Try it: Ninety-seven percent of the council voted yes, so the other side barely counted. Which phrase fits a formal report? (an overwhelming majority / a big majority / a tall majority) Answer: an overwhelming majority — 'Overwhelming' says the majority was so large the other side barely registered, which is what ninety-seven percent means. 'Big majority' is understood but too casual for a formal report, and 'tall majority' isn't an English pairing at all.
Try it: Which phrase describes an intense, emotional argument in formal English? (a heated debate / a hot debate / a boiling debate) Answer: a heated debate — All three reach for the same heat image, but English settled on 'heated' as the partner for 'debate'. 'Hot debate' and 'boiling debate' are understandable and you may hear them, yet neither is the pairing a formal report uses.
The partner for an idea with no detail
Vague means not clearly defined and not thought through, and it is the partner formal English uses for an idea with no detail behind it. It works across a whole family: a vague notion, a vague idea, a vague sense, a vague recollection, all of them say someone has a rough impression but nothing precise. A casual swap like 'fuzzy notion' is understood, but vague is the one a report wants.
vague notion /veɪɡ ˈnoʊʃən/ — The early plans rested on a vague notion of what the neighborhood needed.
Not ""Experts have a fuzzy notion of when the change will happen." (understood, but non-standard in formal writing)" — say ""Experts have a vague notion of when the change will happen." (the fixed collocation)". Notion partners with vague when the idea is unclear. 'Fuzzy' belongs to speech, not to a report, even though a reader would follow it.
Try it: A report describes an idea that nobody has pinned down yet. Which phrase fits? (a vague notion / a fuzzy notion / a weak notion) Answer: a vague notion — 'Vague' is the partner a report reaches for when an idea has no clear detail behind it. 'Fuzzy notion' carries the same meaning but belongs to speech, not a report. 'Weak notion' judges how convincing the idea is rather than how clearly it is defined, so it answers a different question.