Idaho Fish and Game does not have a specific definition of a compound bow. However, on page 76 of the Idaho Big Game Seasons & Rules brochure for 2012 explains what archery equipment would be unlawful to pursue or kill big game with. I have copied and pasted this section below.
In any hunt, including general any-weapon seasons and shortrange
hunts, it is unlawful to pursue or kill big game animals:
• With arrows or bolts having broadheads measuring less
than 7/8 inch in width and having a primary cutting edge
less than 0.015 inch thick.
• With any bow having a peak draw weight of less than 40
pounds up to or at a draw of 28 inches.
• With an arrow or bolt wherein the broadhead does not
precede shaft and nock.
• With any chemicals or explosives attached to the arrow or
• With arrows or bolts having expanding broadheads.
• With arrows or bolts having barbed broadheads, which is
a broadhead with any portion of which forms an angle less
than 90 degrees with the shaft or ferrule.
• With any electronic or tritium-powered device attached
to an arrow, bolt or bow. Except disabled archery permit
holders may use a nonmagnifying sight with battery
powered or tritium lighted reticles.
• With any bow capable of shooting more than one arrow at
• With any compound bow set at more than 85 percent letoff.
• With an arrow or bolt, and broadhead with a combined
total weight of less than 300 grains.
• With an arrow less than 24 inches from broadhead to nock
• With a bolt (crossbow) less than 12 inches from broadhead
to nock inclusive.