Weakened is a term that signifies a decrease in strength or vitality. There are a number of synonyms for weakened that can be used to describe this state, such as debilitated, enfeebled, diminished, frail, infirm, exhausted, and vulnerable. Some other synonyms that come to mind include feeble, powerless, worn out, fatigued, faint, and soft. Each of these synonyms has a slightly different connotation, so the choice of the right word depends on the context and the level of weakness being described. However, all these synonyms can be used interchangeably with the word weakened to convey the idea of a loss of power or vitality.