Refers to the faculty of reasoning and understanding, often contrasted with emotion or instinct.
Intellect alone cannot move people's hearts.
He is a person of superior intellect.
理性 means 'reason' as a faculty, often contrasted with emotion; 理知 is closer to 'intellect' as the power of knowing and thinking.
Standard kanji form for intellect/intelligence.
Alternate kanji form; 智 is a variant of 知.
Compound of 理 (reason, logic) and 知 (knowledge, wisdom). The exact historical derivation is uncertain, but the combination naturally yields the meaning of intellect or intelligence.