1. (n.) A kind of small shield or buckler, used as a defensive weapon in war.

2. (n.) A butt or mark to shoot at, as for practice, or to test the accuracy of a firearm, or the force of a projectile.

3. (n.) The pattern or arrangement of a series of hits made by a marksman on a butt or mark; as, he made a good target.

4. (n.) The sliding crosspiece, or vane, on a leveling staff.

5. (n.) A conspicuous disk attached to a switch lever to show its position, or for use as a signal.

aim alpha decay atom-chipping atom-smashing atomic disintegration atomic reaction atomization beta decay bombardment breeding bullet butt by-end by-purpose byword byword of reproach chain reaction cleavage derision destination disintegration series dissociation dupe duty end end in view exchange reaction fair game fall guy figure of fun final cause fission fission reaction fool function game gamma decay gazingstock goal goat ionization jest jestingstock joke laughingstock mark mockery monkey neutron reaction nonreversible reaction nuclear fission nucleization object object in mind objective photodisintegration prey proton gun proton reaction purpose pursuit quarry quintain reason for being reversible reaction scapegoat sitting duck splitting the atom stimulation stock teleology thermonuclear reaction toy ultimate aim use victim whipping boy