tall and slim
頎 describes a person's build as tall and slim, with an elegant or well-proportioned appearance.
頎 combines 斤 (axe) and 頁 (head). The exact historical development is uncertain, but it likely originally described a tall, slender appearance, possibly related to the shape of an axe head or the head itself.
Picture a person with a head (頁) as sharp and upright as an axe blade (斤): tall, slim, and elegantly proportioned.
For キ, imagine a tall, slim key (キ) that unlocks a door: its slender shape matches the kanji's meaning.