Use 'feebly' to describe actions done with very little strength, as if one's energy is almost gone. After the long run, he feebly collapsed onto the grass.
Pro Tip 2/3
Lack of Effect
'Feebly' can imply an action is ineffective or unlikely to succeed because of its weakness. The virus spread as people feebly disinfected their hands without soap.
Pro Tip 3/3
Not Forceful
Describing a speech or argument as 'feebly' suggests it lacks forcefulness and impact. He feebly presented his case, making no impression on the jury.