快適
かいてき · kaiteki · JLPT N3 · na-adj
pleasant
🛋️ 快適 = pleasant (快) + suitable (適): it suits you and feels good
快 means pleasant or cheerful, as in 快楽 (pleasure). 適 means suitable or fitting, as in 適切 (appropriate). Something that fits you and feels nice is 快適: a comfortable room, a smooth train ride, agreeable weather.
快 — heart radical 忄 + 夬 (phonetic)
快 is a semantic-phonetic compound. The heart radical 忄 carries the meaning, since the original sense referred to a feeling of pleasure or delight. The right side 夬 supplies the sound. The meaning later extended from 'pleased' to 'quick, fast', the dominant modern sense.