by 1851, "air-tight chamber in which operations are carried on under water," to regulate pressure for the safety of workers, from air (n.1) + lock (n.1) in the canal sense.

1779, "complete standstill," from dead (adj.), in its emphatic use, + lock (n.1). First attested in Sheridan's play "The Critic." By 1808 as "type of lock worked on one side by a handle and the other by a key." Deadbolt as a type of lock also is from 1808.

type of gun lock that uses sparks to ignite the priming, 1540s, from fire (n.) + lock (n.1). Originally of the wheel-lock; transferred 17c. to the flintlock.

also flintlock, 1680s as a type of gunlock in which fire is produced by a flint striking the hammer, from flint + lock (n.1) in the firearm sense.

1980 (n.); 1987 (v.); from grid (n.) + lock (n.1). Related: Gridlocked; gridlocking.

1848, "chains for the legs," from leg (n.) + lock (n.1). As a hold in wrestling, from 1886.

"a box with a lock" (for keeping valuables, etc.), 1855, from lock (n.1) + box (n.1). Earlier as the name of the metal box containing the external lock mechanism on a door.

mid-14c., "iron cross-bar of a window," from Old French loquet "door-handle, bolt, latch, fastening" (14c.), diminutive of loc "lock, latch," from Frankish or some other Germanic source (compare Old Norse lok "fastening, lock;" see lock (n.1)). Meaning "little ornamental case with hinged cover" (containing a lock of hair, miniature portrait, etc.) first recorded 1670s. Italian lucchetto also is from Germanic.

"a maker of locks," early 13c., from lock (n.1) + smith (n.).

1802, in military writing, to describe a very tight style of mass marching, from lock (n.1) + step (n.).

Lock-step. A mode of marching by a body of men going one after another as closely as possible, in which the leg of each moves at the same time with and closely follows the corresponding leg of the person directly before him. [Thomas Wilhelm, "Military Dictionary and Gazetteer," Philadelphia, 1881]

Figurative use by 1836.