BACK is a hinge word: 11 words make a compound in front of it and 13 make one after it, so it can sit in the middle of a chain and hold two compounds together at once.
Each of these makes a compound ending in BACK.
Each of these makes a compound starting with BACK.
BACK is both a body part and a direction, which is why it hinges so freely. As a noun it takes modifiers in front (HORSEBACK, PAPERBACK); as a directional particle it attaches to verbs behind (BACKFIRE, BACKLASH).
Put any word from the first list in front and any word from the second behind, and you have a three-word chain in which both neighbouring pairs join. Here are some of them.
COME → BACK → BOARD — comeback and backboardFALL → BACK → BONE — fallback and backboneFEED → BACK → DOOR — feedback and backdoorFLASH → BACK → FIRE — flashback and backfireHORSE → BACK → GROUND — horseback and backgroundOUT → BACK → PACK — outback and backpackPAPER → BACK → SEAT — paperback and backseatPAY → BACK → SIDE — payback and backsideQUARTER → BACK → STAGE — quarterback and backstageSET → BACK → WARD — setback and backwardTHROW → BACK → WATER — throwback and backwaterKEYSTONE is a free daily puzzle built entirely out of chains like these. You get the two ends and have to fill the two words in the middle. Three bridges a day, no account, no cookies.
Each of these has a page like this one. There is also an index of all 28.
BALL · BED · BOARD · BOOK · BREAK · DAY · DOWN · FALL · FIRE · GUN · HAND · HEAD · HOUSE · LAND · LIFE · LIGHT · MAN · NIGHT · OFF · OUT · OVER · SHIP · SIDE · SOME · TIME · WAY · WORK