Padlock
The last one or more letters of a word or phrase (LEFT) are the same as the first one or more letters of another (RIGHT); joining the remaining letters forms another (LOCK). Examples: LEFT = norther, RIGHT = thermal, LOCK = normal; and LEFT = après-ski, RIGHT = press kit, LOCK = at.
Notice that every letter must be used in exactly two words or phrases.
The combination padlock is the same as the padlock, with the added feature that overlapping LEFT and RIGHT produces a fourth word or phrase (WHOLE). For example: LEFT = scar, RIGHT = Arab, LOCK = scab, WHOLE = scarab.
In the progressive padlock, three or more words or phrases form an overlapping chain; the nonoverlapping pieces at the beginning and end of the chain form another word or phrase. For example: ONE = padre, TWO = retrench, THREE = trenchant, FOUR = anthem, FIVE = hemlock, LOCK = padlock. (If the first and last pieces were combined in the opposite order, this would instead be a cyclegram.)
A lock and drop is a padlock, except that the overlapping letters form a word. Examples: lethal, halter, letter, Hal; tread, readier, tier, read; and coin, Indy, Cody, in. The lock and drop was invented by Wabbit.
WILLz introduced the padlock, based on an Italian puzzle type, at the 1980 convention.