Webster's English Dictionary

weak

weak \'we-k\ aj [ME weike, fr. ON veikr; akin to OE wi-can to yield, L 
   ]vicis change - more at WEEK 1: lacking strength : as  1a: deficient in 
   physical vigor : FEEBLE, DEBILITATED  1b: not able to sustain or exert much 
   weight, pressure, or strain  1c: not able to resist external force or 
   withstand attack  2a: mentally or intellectually deficient  2b: WAVERING, 
   VACILLATING  2c: resulting from or indicating lack of judgment or 
   discernment  2d: not able to withstand temptation or persuasion  3: not 
   factually grounded or logically presented {a ~ argument}  4a: not able to 
   function properly  4b: lacking skill or proficiency : indicative of a lack 
   of skill or apti tude 4c: wanting in vigor of expression or effect  5a: 
   deficient in the usual or required ingredients : DILUTE {@ coffee} 5b: 
   lacking normal intensity or potency {~ strain of virus}  6a: not having or 
   exerting authority or political power {~ governm ent} 6b: INEFFECTIVE, 
   IMPOTENT  of a verb  7: belonging to a conjugation that forms the past 
   tense and past participl e by adding the suffix -ed or -d or -t 8a: bearing 
   the minimal degree of stress occurring in the language {~  syllable} 8b: 
   having little or no stress and obscured vowel sound {'d is the  ~ form of 
   would}DECREPIT mean not strong enough to endure strain, pressure, or 
   strenuous effort. WEAK is of wide application in implying deficiency or 
   inferiority in strength or power of any sort; FEEBLE suggests extreme 
   weakness inviting pity or contempt; FRAIL implies delicacy and slightness 
   of constitution or structure; FRAGILE suggests frailty and brittleness 
   unable to resist rough usage; INFIRM suggests instability, unsoundness, and 
   insecurity due to old age or crippling illness; DECREPIT implies being worn 
   out or broken down from long use or old age - weak.ly av SYN syn WEAK, 
   FEEBLE, FRAIL, FRAGILE, INFIRM,