GUARD is a hinge word: 3 words make a compound in front of it and 2 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 GUARD.
Each of these makes a compound starting with GUARD.
GUARD and WARD are the same ancient word borrowed twice. Germanic wardon came into English directly as WARD, then returned centuries later through Old French garde as GUARD, so a LIFEGUARD and a WARDEN are cousins several removes apart. BLACKGUARD, once the name for a household's kitchen servants, drifted all the way to an insult.
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.
BLACK → GUARD → HOUSE — blackguard and guardhouseBODY → GUARD → ROOM — bodyguard and guardroomKEYSTONE 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 60.
AWAY · BACK · BALL · BED · BLACK · BOARD · BOAT · BOOK · BOY · BREAK · CHECK · CROSS · DAY · DOOR · DOWN · FALL · FATHER · FIRE · FOOT · GROUND · GUN · HAND · HEAD · HOOD · HOUSE · LAND · LESS · LIFE · LIGHT · LINE · LOAD · MAN · MOTHER · NIGHT · OFF · OUT · OVER · PAY · POINT · POST · POWER · ROOM · RUN · SET · SHIP · SIDE · SOME · STEP · SUN · TAKE · TIME · TURN · UNDER · WALK · WARD · WATER · WAY · WOOD · WORK