latch / lach/ • n. a metal bar with a catch and lever used for fastening a door or gate. ∎  a spring lock for an outer door that catches when the door is closed and can only be opened from the outside with a key. ∎  Electr. a circuit that retains whatever output state results from a momentary input signal until reset by another signal. ∎  the part of a knitting machine needle that closes or opens to hold or release the wool.• v. [tr.] fasten (a door or gate) with a latch: she latched the door carefully. ∎  [intr.] Electr. (of a device) become fixed in a particular state.PHRASAL VERBS: latch onto inf. attach oneself to (someone) as a constant and usually unwelcome companion: a knack for latching onto people with greater initiative and enterprise. ∎  take up (an idea or trend) enthusiastically: the media have latched onto the snappy “Generation X” catchphrase. ∎  (of one substance) cohere with (another).

latch An electronic device that can store temporarily a single bit of data. It can be considered as an extension of a simple flip-flop. The storage is controlled by a clock signal, a given transition of which fixes the contents of the latch at the current value of its input. The contents will remain fixed until the next transition of the clock.

latch
A. (dial.) loop, noose;

B. fastening for door or gate. XIV. In sense A prob. var. of LACE (OF. var. lache of laz); in sense B prob. f. (dial.) latch vb. OE. læċċan seize, grasp, perh. rel. to Gr. lázesthai.