Definition
To restrict is to hold something inside limits — to cut down how much is allowed through, who may enter, or how far a thing can go. A diet restricts certain foods; a law restricts access; a narrow valve restricts a flow to a trickle. The point is throttling rather than stopping: what is restricted still exists, but only a permitted portion gets past. From the Latin restringere, 'to bind back', it shares its root with 'restrain' and 'strict'.
Examples
Collocations
restrict access·severely restrict·restrict movement·restricted to·restrict the flow
Synonyms
limit·confine·curb·constrain·restrain
Antonyms
broaden·permit·free
Word family
restriction (noun)·restricted (adjective)·restrictive (adjective)
In TOEFL & IELTS
A core academic verb for policy and science writing — 'restrict access to', 'severely restrict', 'restricted to' are exam-ready. Promote the noun restriction and the adjective restrictive in formal essays. Note that it is weaker than ban or prohibit: to restrict is to limit, not to forbid outright, which matters when you are weighing arguments.