compulsory
a.強迫的，強制的(compelling, obligatory, required)
→ com- , together ; plus , pel , to drive

dormitory
n.宿舍 → dorm , to sleep
→ dormant a.睡眠狀態的；休止的，不動的

factory
n.工廠(plant)；製造廠 → fact , fac , to make

illusory
a.虛幻的 → illus , to mock欺騙，愚弄
→ illusive a.虛幻的；欺騙的，迷惑的

laudatory
a.讚賞的(commendatory)
→ laudable a.值得讚美的(commendable, creditable, praiseworthy)

lavatory
n.盥洗室；廁所 → lav , to wash
→ lavish a.消費的(prodigal)；豐富的(abundant)

puragatory
n.煉獄；滌罪所 → pur , clean ; (a)g , to do
→ purgatiive n.(醫)瀉藥