Dic: lock// have a lock on something

a lock:

─. [US informal, singular] complete control of something

• He appears to have a lock on the nomination for governor. [= he appears to be sure of getting the nomination for governor]
• He has been able to get a lock on the nomination.
• There seems to be no danger that the company will lose its lock on the industry.

─. [US informal, usu singular] someone or something that is certain to have or do something.

• He's a lock for the nomination. = He's a lock to get the nomination. [= he is certain to get the nomination]
• The team is a lock to win the championship.

─. [count, usu singular] something that is certain to happen.

• It looks like his nomination is a lock.

─. a lock on sth: AmE. complete control of something.

• Pro football still has a lock on male viewers aged 18 to 34.

─. a secure hold or grip.

• The distributor has a lock on most of the market.

─. have/get a lock on something: to have/get total control of something or understand it completely.

• Both factions thought they had a lock on the latest trend.

......... Merriam-Webster Learners', LDOCE, American Heritage, Macmillan