1. adjective /ˈsɪli/
A silly man, in simple weedes forworne, / And soild with dust of the long dried way; / His sandales were with toilesome trauell torne, / And face all tand with scorching sunny ray [...].
b) irresponsible, showing irresponsible behaviors.
For, if we justly call each silly man / A little island, What shall we call thee than?
2. noun /ˈsɪli/
a) A silly person; a fool.
b) A mistake.
Wikipedia foundation.