WordNet sense 1 (a spontaneous loss of consciousness caused by insufficient blood to the brain):

swoon, syncope, deliquium

WordNet sense 2 (weak and likely to lose consciousness):

light, lightheaded, light-headed, swooning

WordNet sense 3 (affected by an impairment of normal physical or mental function):

ill, sick

WordNet sense 4 (lacking strength or vigor):

feeble

WordNet sense 5 (having little physical or spiritual strength):

weak

WordNet sense 6 (capable of being perceived by the mind or senses):

perceptible

WordNet sense 7 (lacking clarity or distinctness):

dim, shadowy, vague, wispy

WordNet sense 8 (not clearly defined or easy to perceive or understand):

indistinct

WordNet sense 9 (lacking conviction or boldness or courage):

fainthearted, timid, faint-hearted

WordNet sense 10 (lacking courage; ignobly timid and faint-hearted):

cowardly, fearful

WordNet sense 11 (pass out from weakness, physical or emotional distress due to a loss of blood supply to the brain):

conk, pass out