Definition - one who does things in a small way; tightwad, cheapskate
Piker can refer to a tightwad, a cheapskate, or basically anyone who does not like to spend or give money. One theory on the word's origin connects it to a nickname given to Missourians in the 19th century around the time of the 1849 Gold Rush. A county or two to the north of St. Louis on the Mississippi is Pike County, Missouri, and directly across the river from it is Pike County, Illinois; both counties, in the past, supposedly had a large population of yokels, many of which headed for California to seek a better life. This migration was memorialized in folk songs, such as "Sweet Betsey from Pike":
Oh don't you remember sweet Betsey from Pike, / Who crossed the big mountains with her lover Ike, / With two yoke of cattle, a large yellow dog, / A tall Shanghai rooster, and one spotted hog; / Saying goodbye, Pike County, / Farewell for a while; / We'll come back again / When we've panned out our pile.
— Carl Sandburg, The American Songbag, 1927
We can't say whether the unflattering characterization of Pike Countians as yokels was deserved or not, and we have no idea as to what incidents caused them to be despised by Californians. However, we do know that, for whatever reason, Californians developed a marked antipathy for Missourians and expressed their dislike for them by using Piker (also Pike) as a pejorative term. As example, an 1857 publication explained Pike as "a household word" in San Francisco used to designate people with "a happy compound of verdancy and ruffianism."
From being a term for a Missourian who migrated to California exhibiting undesirable social characteristics, piker was broadened as a general term of contempt for other migrants to California and later was applied, still pejoratively, to various kinds of small-time gamblers.
Nowadays, when encountered, Piker is used of a person of mean and petty habits or outlook and to people noted for their unwillingness to spend money or pay their fair share. The connection with Pike County, Missouri, is all but forgotten except by etymologists.
To get a better sense of just how much money, let's take a virtual stroll down K Street and see what everyone is spending on the world's second-oldest profession. It's all laid out for us by OpenSecrets.org. The defense lobby? Pikers. They contributed $24 million to individuals and PACS during the last election cycle. The farm lobby? $65 million. Health care? We're getting warmer. Health care was the No. 2 industry, at $167 million.
— Kevin Drum, Mother Jones, January/February 2010