Faible, adj : weak, feeble, frail, flimsy, fragile.
avoir un faible pour : to have a weakness for, to have a soft spot for.

Il a été très malade, il est encore faible.
He has been very ill and he’s still weak.

Elle parlait d’une voix si faible, on l’entendait à peine.
She was speaking in such a feeble voice that you could hardly hear her.

Est-ce que tu as vu sa grand-mère ? Elle has l’air très faible.
Have you seen his grandmother? She looks very frail.

Cette corde est trop faible pour supporter ce poids.
This rope is too flimsy to hold the weight.

Je me sens encore faible.
I still feel a bit fragile.