From Longman Dictionary of Contemporary Englishlock armslock armsHOLDif people lock arms, they join their arms tightly with the arms of the people on each side The police locked arms to form a barrier against the protesters. → lock
Examples from the Corpus
lock arms• This is not to say that Brownmiller has written a sanguine portrait of sisters locking arms in struggle.• Fifty students locked arms to block the entrance to the building. 