庇を貸して母屋を取られる
(Hisashi wo kashite omoya wo torareru;
“Lending the eaves, having the main room taken”)

Definition:

Giving someone an inch, only for them to take a mile. Lending or giving someone part of something, especially when that person is in need of help, only to have them take the whole thing. Literally, lending someone (the use of) the eaves of a traditional Japanese estate – or rather, the narrow raised walkway that runs around the outside of the house and is protected from the elements somewhat by its eaves – only to have them take advantage and occupy the main room of the central building. Somewhat less-used secondary meanings are to be harmed in some way by a guest, or to have one’s kindness met with enmity.

Breakdown:

This saying comprises a pair of verb phrases. The first verb is 貸す (kasu), “to lend” or “to rent out,” in conjunctive form, with the particle を (wo) marking as its direct object the noun 庇 (hisashi), the eaves and/or raised walkway that run around the outside of a traditional Japanese estate-home. The second verb is 取る (toru), “to take,” in passive sentence-final form, again with the particle を showing that it acts on the noun 母屋 (omoya), literally “mother roof” but in this case signifying the central space of the estate.

Notes:

庇 can also be written 廂, and 母屋 can also be written 母家, without any change in meaning or pronunciation. 庇 may also be replaced with synonym 軒 (noki), although the latter is more commonly used to refer to the eaves of a modern, Western-style house.

Example sentence:

「百円貸してって頼まれていいよと答えたけど、知らないうちに財布を引っ掻き回されたよ。庇を貸して母屋を取られると思わなかったわ」

(“Hyakuen kashite tte tanomarete ii yo to kotaeta kedo, shiranai uchi ni saifu wo hikkaki mawasareta yo. Hisashi wo kashite omoya wo torareru to omowanakatta.”)

[“She said ‘Loan me a hundred yen,’ and I said ‘Okay,’ and next thing I knew she’d rifled through my whole wallet! I never thought I’d give her an inch and she’d take a mile.”]