Peckish \PEK-ish\ , adjective;
1. Somewhat hungry
2. Rather irritable
Peckish, meaning "disposed to peck, somewhat hungry," dates to 1785 from the verb peck (as in, 'The hen pecked the ground'). It dates to the 1300's and is either a variation of picken ("to peck", the forebear of pick) or comes from Middle Late German pekken ("to peck with the beak").
There is another form that dates to the late 13th century. It's a noun meaning "dry measure of one-quarter bushel" and it's origins are unknown, but it may be connected to Old French pek or picot. The origins of the French words are also unknown.