意 stacks 音 (sound) over 心 (heart): the heart's sound — what you mean before you say it. Few characters define themselves so poetically: intention is the voice inside the chest.
意 carries Chinese's inner life: 意思 (meaning — and much more), 同意 (agree: same-intention), 满意 (satisfied: full-hearted), 有意思 (interesting: has meaning). The phrase 不好意思 ('embarrassed / excuse me') is the everyday social lubricant. And 意思 itself is famously slippery: 小意思 (a trifle/small gift), 不够意思 (not loyal enough as a friend), 有点意思 (getting interesting) — a whole social code in one word.
The sound 音 of the heart 心 — what you MEAN.
The untranslatable ladder of 意思: 有意思 interesting → 小意思 no big deal → 不好意思 embarrassed → 不够意思 not a true friend.