1. to take possession of (forcibly); to take over (a company, account, etc.); to capture (a castle, enemy position, etc.); to seize; to occupy; to usurp
彼は会社を乗っ取ったとか。I hear he took over the company.
2. to hijack (a plane, ship, etc.)
犯人は飛行機を乗っ取った。The criminal hijacked a plane.