in·firm 
(ĭn-fûrm)
(ĭn-fûrm)adj.
1. Weak in body or mind, especially from old age or disease. See Synonyms at weak.
2. Not strong or stable; shaky: an infirm foundation.
3. Archaic Lacking firmness of will, character, or purpose; irresolute.
[Middle English infirme, from Old French, from Latin īnfirmus : in-, not; see IN-1 + firmus, strong, firm; see dher- in the Appendix of Indo-European roots.]
in·firmly adv.