pennywhistle

As nouns the difference between whistle and pennywhistle

is that whistle is a device designed to be placed in the mouth in order, or driven by steam or otherwise, to make a whistling sound while pennywhistle is a six-holed flute-like instrument with a fipple they have approximately a two octave range (sometimes a little higher) stereotypically, they are made out of tin, but in reality they come in all sorts of varieties, including tin, brass, nickel, cane, polymer, etc.

As a verb whistle

is (ambitransitive) to make a shrill, high-pitched sound by forcing air through the mouth to produce a whistling sound, restrictions to the flow of air are created using the teeth, tongue and lips.