www.alphadictionary.com

A lock for a door can be integral or separate (e.g., a padlock). To secure it, there's the verb "lock". The door in question can be "locked" or "unlocked".

In a canal, a lock is a segment that can be segregated from the main flow, allowing the water level to be raised or lowered, so that a vessel in the lock can get around an otherwise unnavigable stretch of the main waterway. Again a verb: "lock through". And an adjectival prefix: "lockmaster".

A snippet of hair, as in "The Rape of the Lock", a poem by Alexander Pope, or held as a keepsake in a locket. (No verb that I'm aware of.)

An intangible analogue of the first sense, as in "a lock on an account"; again a verb.

A type of firearm: "flintlock" or "percussion lock". In this regard, Slava has asked about "lock and load", q.v.

How might these be related?

Don't forget headlock.

And lockjaw. And vapor lock. Locksmith should already be covered.
One locks up a forme for a printing press, and the hoosegow is a lockup.

Thank you, Slava, for jogging my memory.

And what about a lock-down - such as Australia is currently enjoying?

Or a lock-up that Nelson Mandela endured for 25 years?

Or a lock-out that British coal-miners have suffered in times gone by?

Or a lock-in that fixes a date in our diaries for a particular event?

Or a lock-away that keeps things safe for retrieval later?