楔 alone is the character, but in everyday speech it most commonly appears as 楔子 (xiēzi), meaning a wedge or peg. 楔形 means wedge-shaped, as in 楔形文字 (cuneiform writing).
Wood radical on the left, a pictograph of a tree. Indexes 楔 in the wood-object family with 板 board, 桩 stake, 柱 pillar. Marks the character as a wooden implement; combined with the cutting imagery on the right, narrows to a tapered block used to split or secure.
Right side 契 supplies the sound through a drift: qì to xiē. 契 originally pictured a knife 刀 cutting tally marks into a surface, the act of incising. That cutting imagery doubles as a faint semantic hint: a wedge is what you drive into a cut to widen it.
