MUD
FORTY (was the first!)
ABHORS - ADEPT - ADOPT - ALMOST - BEGIN - BEGINS - BELOW - -BENT - BEST - BOP - CHIMPS - CHINTZ - DEHORT - DEITY - DELTA - DENY - DIRTY - DRAB - EGAD - EGO - EGOS - ELM - EMPTY - EMU - END - ENVY - ERA - ERST - ETA - EVAC - GILT - GLAD - GLOVE - GLOW - GRAB - HI - HIDE - HIJAB - HINZE - HORDE - HORSE - INCH - KEG - KNOB - KNOT - KNOW - KOB - KORA - LAB - LEG - LIKE - LOACH - LOAD - LOCK - LORD - LOST - LOVE - LOW - LUCK - MODEL - MORAL - MOREL - MORSEL - MORTAL - MOST - MOTH - MUCH - MUD - NAIL - NOPAL - NOPE - NORSE - NORTH - NOVEL - NUDE - OPEN - ORACH - OUCH - OVEN - OVAL - OWL - PACK - PALM - PEG - PRIM - PRUDE - PSALM - PSYCHO - PUCE - PUCK - QUACK - RACK - RADIO - RAMP - RUDE - SAD - SAILOR - STACK - STAMP - STAR - STEM - STOP - STUCK - STUDIO - STUDY - STUMP - SWAG - SWAMP - SWAN - SWAP - TACKS - TAGS - TAIL - TAILORS - TAMPS - TENOR - THIN - TINS - TUBER - TUBERS - TUDORS - TUG - TUMORS - TUX - TWAIN - UART - UP - UZBEKS - WADERS - WHILST - WHIM - WHIST - XU - YACHT - YAM - YELP - YET - YOU - ZIP