said of food: tasteless or unpalatable from age
said of air: musty or foul
said of news: no longer fresh or interesting
tedious from familiarity
stale jokes
said of a cheque or debt: no longer valid because out of date
impaired in vigour or effectiveness, from overexertion or repetitiveness
stalely adv
staleness noun
[Middle English, orig describing ale which had become clear and strong with standing, prob via Anglo-French from Old French estaler to come to a standstill, from estal place, position, of Germanic origin]