true intention; real motive
Refers to one's hidden or underlying intention, often used in contexts where someone's true feelings or plans are not openly expressed.
彼の奥意を探るのは難しい。
It's difficult to discern his true intentions.
Compound of 奥 (inner depths) and 意 (mind, intention). The exact historical derivation is uncertain, but the meaning is transparent from the kanji.