weakShe was too tired and weak to finish the race.
feebleMany of the pensioners were so feeble they had to be stretchered onto the ship.
weedyUKinformaldisapprovingI was just this weedy guy who always had his head in a book.
frailA frail, grey-haired lady walked slowly down the street.
ailingHe shared an apartment with his ailing mother.
dodderymainlyUKinformalJudges are often portrayed as doddery old men.
sicklyHe was a sickly child.
defencelessUKHow could anyone hurt a small, defenceless child?
vulnerableThe disease most often affects vulnerable people such as children and the elderly.
faintIf you feel faint, sit down with your head between your knees.
fragileThey'd all had a few beers the night before and were feeling a bit fragile.