sweet
甜 centers on the sensation of sweetness, especially in taste. It is a direct character for describing something as sweet.
甜 combines 舌 (tongue) and 甘 (sweet), directly expressing the idea of a sweet taste perceived by the tongue.
The tongue 舌 tastes something sweet 甘. Together they make 甜, the character for sweet.
For テン, imagine a sweet treat so good you give it a perfect ten out of ten: ten -> テン, and your tongue confirms it's sweet.