Other forms: locked, locks, locking
A lock is the fastening in a door or a case that only the right key opens. Turn the lock, change the locks, a bicycle lock.
The verb is just as common and takes several particles: lock up the house, lock somebody in, lock somebody out, lock away the valuables. From the physical fastening come a set of figurative uses — locked in a contract, locked in an argument — all meaning unable to get out. Two unrelated senses share the spelling: a lock on a canal is a chamber with gates that raises or lowers a boat, and a lock of hair is a curl. Only the canal one is likely to catch a learner out.
1nounlockA fastening opened with a key or a code.
“The lock on the back door has never worked properly.”
2verbfastenTo fasten something with a lock.
“Lock the shed before you come in.”
3nounsectionA section of canal with gates, used to raise or lower boats.
“There are fourteen locks on that stretch.”
4nouncurlA piece or curl of hair.
“A lock of hair kept in an envelope.”
Too few real examples of this word to estimate which sense is commonest.
lock is a fastening.
Old English loc meant a fastening, and the same root gives Old Norse lok, a lid. The canal sense comes from the same word by way of an enclosure that shuts; the hair sense is a separate Old English word, locc, that happened to fall together with it.
Middle English
lok
English, today
lock
From Middle English lok. From Middle English lok, from Old English loc, from Proto-West Germanic lok, from Proto-Germanic luką from Proto-Indo-European lewg- (“to bend; turn”). Cognate with cim loch, lòch (“hole”), Dutch lok (“hole”), German Loch (“hole”), German Low German Lock (“hole”), lb Lach (“hole”), wym łöch (“hole”), Yiddish לאָך (“hole”), Danish låg (“lid, cover”), Norwegian Bokmål lokk (“lid, cover”), Norwegian Nynorsk lok, lokk (“lid, cover”).
Etymology from Wiktionary, CC BY-SA