Answer:
Concentrate/ concentrated.
Step-by-step explanation:
Opposite meanings of words are the antonyms. Antonyms, in simple terms, are the words that mean the exact opposite of what is being said. While synonyms give the same meaning, antonyms do the opposite.
The given word "dilute" is a verb that means "to make something weaker", to decrease the 'strength' of the thing by adding other things. So, its opposite word will be "concentrate", which means without any addition. We use the word "concentrated" to talk about a strong solution or 'thing'.
Thus, the opposite meaning of 'dilute' is 'to concentrate'.