guardverb
Details of the terms of the negotiation were closely guarded to ensure the best chance of success.
The owner has kept the turnover of the business a closely guarded secret.
The precise statistics are closely guarded, but they have released some limited information.
The formula for the product has been closely guarded for decades.

SMART Vocabulary: related words and phrases

Defending and protecting
air defence
anti-bug
anti-mosquito
baby
bandobast
cocoon
defensive
duck and coveridiom
embedded
featherbedding
fight back
foot patrol
hedge
insulate
poisonous
security light
self-protective
self-protectiveness
shelter
sheltered