偏芯[henshin] eccentricity (in mechanics, electronics, etc.)
燈芯[toushin] (lamp) wick
帯芯[obishin] thick obi sash
摘芯[tekishin] thinning (buds and branches)
芯地[shinji] padding

替え芯[kaeshin] spare lead
鉛筆の芯[enpitsunoshin] lead of a pencil
硬の芯[kounoshin] hard pencil lead
林檎の芯[ringonoshin] core of an apple

鍵を掛ける[kagiwokakeru] to lock
鍵穴[kagiana] keyhole
鍵盤[kenban] keyboard (e.g. piano, computer)
黒鍵[kokken] black keys
打鍵[daken] keystroke

合鍵[aikagi] duplicate key
鍵っ子[kagikko] latchkey child
鍵束[kagitaba] bunch of keys
関鍵[kanken] locking doors