noun
Slang term for a police detective, used in casual or rough speech. Often heard in crime dramas and among criminals or police in fiction.
See also: 刑事
あのデカはやり手だな。
That detective is a sharp one.
デカが張り込んでるから気をつけろ。
The cops are staking out, so be careful.
Standard, neutral term for a police detective. デカ is slang and carries a rougher, more informal tone.
Said to derive from reversing the syllables of 刑事 (けいじ → じけい) and then further altering to でか, but the exact origin is uncertain.