Word Study
g-man
CIDE DICTIONARY
g-man, n. [from Government man.].
A special law-enforcement agent of the Federal Bureau of Investigation. [WordNet 1.5]
OXFORD DICTIONARY
g-man, n. (pl. G-men)
1 US colloq. a federal criminal-investigation officer.
2 Ir. a political detective.
1 US colloq. a federal criminal-investigation officer.
2 Ir. a political detective.
Etymology
Government + MAN
For further exploring for "g-man" in Webster Dictionary Online