speculative spirit; gambling instinct
Refers to a person's inclination toward speculation, risk-taking, or gambling, often in financial or adventurous contexts.
He has a strong speculative streak and got into stocks.
People with a gambling instinct tend to get hooked on gambling.
Compound of 山 (やま, 'mountain', here metaphorically 'speculation' or 'chance') and 気 (け, 'spirit' or 'inclination'), with a geminate consonant inserted. The exact derivation is uncertain, but it likely originated from the idea of 'mountain' as something unpredictable or risky.