yojijukugo (four-character idiom)usually written using kana alone
Describes rushing into something with single-minded, almost reckless determination, ignoring obstacles or consequences. Often used with verbs of action like 進む, やる, or 突き進む.
必死に means 'desperately' or 'with all one's might' and is more common and neutral; しゃにむに adds a nuance of recklessness or ignoring everything else.
Etymology
A yojijukugo of uncertain origin. The kanji 遮二無二 are ateji (phonetic equivalents) and do not contribute to the meaning. The word likely derives from a mimetic or sound-symbolic root, but the exact derivation is unclear.
