There are a total of 35 10-letter words containing 'by', and the number may vary in different dictionaries. You can specify the dictionary and order.

• babyboomer ₂₄
• babyfather ₂₃
• babymother ₂₃
• babysitter ₁₈
• babywalker ₂₆
• boobytraps ₂₁
• byelection ₂₀
• byproducts ₂₃
• byssinoses ₁₆
• byssinosis ₁₆
• bystanders ₁₇
• cubbyholes ₂₅
• hobbyhorse ₂₂
• hypabyssal ₂₃
• labyrinths ₁₉
• lullabying ₂₂
• presbyopes ₂₁
• presbyopia ₂₁
• presbyopic ₂₄
• presbyters ₁₈
• presbytery ₂₀
• rubythroat ₁₈
• subshrubby ₂₅
• yottabytes ₁₇
• zettabytes ₂₄
• babyproofs ₂₂
• bobbysocks ₂₅
• bobbysoxer ₂₆
• brontobyte ₁₇
• byssaceous ₁₇
• bytownites ₁₈
• hushabying ₂₂
• moucharaby ₂₂
• presbytism ₁₉
• tabbyhoods ₂₁

There are 35 10-letter words containing by in the well-known word game dictionary, 19 in the Scrabble US (US/Canada/Thailand - TWL/NWL) dictionary, and 28 in the Scrabble UK (International - SOWPODS/CSW) dictionary, and 25 in the Words with Friends (WWF) dictionary.