航こう空くう発はつ動どう機き

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Meanings

aircraft engine

Technical term for an engine that powers an aircraft. Used in aviation contexts.

エンジン
エンジン is a general term for any engine (car, machine, etc.), while 航空発動機 specifically refers to an aircraft engine.
航こう空くう機き
航空機 means 'aircraft' (the vehicle), while 航空発動機 is the engine that powers it.

航こう空くう発はつ動どう機き
Standard modern spelling.
航こう空くう發はつ動どう機き
out-dated kanji form
Contains outdated kanji 發 (old form of 発); rarely used today.

Compound of 航空 (aviation) + 発動機 (engine). 発動機 itself is a somewhat older term for 'engine', now often replaced by エンジン in everyday language.