ADEPT

FORTY (was the first!)
ADEPT - ADOPT - ALMOST - BOP - BEGINS - BELOW - BEST - CHIMPS - CHINTZ - DELTA - DRAB - DENY - EMPTY - EGAD - EGO - ELM - EMU - ERA - ERST - EVAC - ETA - ENVY - GLAD - GILT - GRAB - HAM - HINZE - HIDE - HORDE - HORSE - KNOW - KNOB - KEG - LOVE - LIKE - LAB - LEG - LOACH - LUCK - LOST - MOTH - MODEL - MORSEL - MORTAL - NAIL - NOPE - NOPAL - NORSE - NORTH - NOVEL - OPEN - OUCH - OVEN - OWL - OVAL - ORACH - PEG - PUCE - PSYCHO - PACK - PSALM - QUACK - RACK - RADIO - RUDE - STAR - SAD - STUDY - STAMP - STUMP - STUDIO - SAILOR - SWAMP - SWAN - TAILORS - THIN - TWAIN - TUBER - TUBERS - TUDORS - TUMORS - TENOR - UART - UP - WATERS - WHILST - YACHT - YELP - YOU - ZIP