weak as a kitten

(as) weak as a kitten

Especially weak, feeble, and vulnerable; completely unable to defend oneself. The heart attack left me bedridden and weak as a kitten for nearly a month. Tom's always been as weak as a kitten, so we don't bother trying to roughhouse with him at all.
See also: kitten, weak
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

weak as a kitten

Feeble and fragile, as in After that bout with flu she was weak as a kitten. This simile has largely replaced weak as a cat, from the early 1800s.
See also: kitten, weak
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

weak as a kitten

Feeble, defenseless. This proverbial simile goes one better than weak as a cat, dating from the early nineteenth century. Erle Stanley Gardner had “He felt as weak as a kitten” in The Case of the Drowsy Mosquito (1943). Other variations are O. Henry’s weak as a vegetarian cat (Cupid à la Carte, 1907) and weak as a newborn kitten.
See also: kitten, weak
The Dictionary of Clichés by Christine Ammer Copyright © 2013 by Christine Ammer
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References in periodicals archive ?
From being in rude good health for the pairs events, he woke up on Sunday as weak as a kitten and with a high temperature but he refused to pull out, shot five birdies on the front nine and just about hung on, despite feeling exhausted, to close out Chris DiMarco on the final green.