Synonyms and antonyms are common vocabulary skills in 11+ preparation. The goal is not just to memorise long word lists: children need to understand how a word behaves in context and recognise the closest meaning.
Synonym strategy
First decide what the word means. Then look for the option with the closest meaning, not simply a word from the same topic. For example, rapid and swift are close in meaning, while race is related but not a synonym.
Antonym strategy
Ask yourself: what is the direct opposite? Watch for near-opposites and words that are related but not true opposites.
Learn words in groups
Group vocabulary by meaning, emotion, movement, size, character and description. Learn a word with a definition, synonym, antonym and example sentence. Then use it in your own sentence.
Daily practice
Ten focused words a day can be more useful than trying to memorise a huge list at once. Revisit older words using spaced repetition so they move into long-term memory.