WordNet sense 1 (not tense or taut):

loose, slack

WordNet sense 2 (lacking in strength or firmness or resilience):

flaccid, limp

WordNet sense 3 (having little physical or spiritual strength):

weak

WordNet sense 4 (characterized by neglect and undue lack of concern):

negligent

WordNet sense 5 (not constipated):

regular, unconstipated