There are a total of 104 9-letter words containing 'rain', and the number may vary in different dictionaries. You can specify the dictionary and order.

• birdbrain ₁₇
• braincase ₁₆
• braincell ₁₈
• braindead ₁₅
• brainfood ₁₇
• brainiacs ₁₆
• brainiest ₁₃
• brainless ₁₄
• brainpans ₁₇
• brainsick ₂₀
• brainstem ₁₆
• brainwash ₁₈
• brainwave ₂₀
• brainwork ₂₀
• constrain ₁₄
• detrained ₁₂
• distrains ₁₁
• distraint ₁₁
• drainages ₁₃
• draincock ₂₁
• drainpipe ₁₇
• endbrains ₁₅
• engrained ₁₄
• entrained ₁₂
• entrainer ₁₁
• eyestrain ₁₂
• foodgrain ₁₆
• forebrain ₁₆
• grainiest ₁₂
• grainless ₁₃
• grosgrain ₁₄
• hindbrain ₁₇
• ingrained ₁₄
• lamebrain ₁₇
• midbrains ₁₇
• migraines ₁₅
• mistrains ₁₃
• overtrain ₁₄
• pretrains ₁₃
• quatrains ₂₀
• rainbands ₁₅
• rainbirds ₁₄
• raincheck ₂₂
• raincoats ₁₃
• raindance ₁₅
• raindrops ₁₄
• rainfalls ₁₅
• rainflies ₁₄
• raininess ₁₁
• rainmaker ₁₇
• rainproof ₁₆
• rainspout ₁₄
• rainstorm ₁₃
• rainswept ₁₆
• rainwater ₁₃
• rainworms ₁₆
• refrained ₁₄
• restrains ₁₀
• restraint ₁₀
• retrained ₁₁
• seatrains ₁₀
• spraining ₁₆
• strainers ₁₀
• straining ₁₃
• substrain ₁₄
• suzerains ₂₀
• trainable ₁₄
• trainband ₁₅
• trainfuls ₁₅
• trainings ₁₃
• trainload ₁₂
• trainsets ₁₀
• trainshed ₁₃
• trainsick ₁₇
• trainways ₁₅
• undrained ₁₄
• untrained ₁₃
• woodgrain ₁₆
• chamfrain ₁₉
• drainable ₁₂
• feedgrain ₁₄
• peabrains ₁₃
• rainstick ₁₅
• rainsuits ₉
• refrainer ₁₂
• retrainee ₉
• trainless ₉
• aerotrain ₉
• brainfart ₁₄
• darrained ₁₁
• darraines ₁₀
• engrainer ₁₀
• filigrain ₁₃
• grainages ₁₁
• grainings ₁₁
• murrained ₁₂
• outstrain ₉
• overgrain ₁₃
• rainbowed ₁₅
• raindates ₁₀
• raintight ₁₃
• rainwears ₁₂
• riverains ₁₂
• uptrained ₁₂

There are 104 9-letter words containing rain in the well-known word game dictionary, 73 in the Scrabble US (US/Canada/Thailand - TWL/NWL) dictionary, and 88 in the Scrabble UK (International - SOWPODS/CSW) dictionary, and 78 in the Words with Friends (WWF) dictionary.