1. big gun - Noun
2. big gun - Phrase
an important influential person
Source: WordNetbig-gun
Your heaviest artillery will be your will to live. Keep that big gun going. Norman Cousins
Jenna stumbled backward, her eyes on the woman who slammed the door behind her with one foot while both hands held a gun. A big gun. Pointed right at Jenna. Lis Wiehl
There's not a big gun culture in England at all still. Clive Owen
he thinks he's a big shot Source: Internet
she's a big deal in local politics Source: Internet
the Qaeda commander is a very big fish Source: Internet