you could have knocked me down with a feather

Related to you could have knocked me down with a feather: You could have knocked me over with a feather, knock me over with a feather

you could have knocked me down with a feather

An expression of great or utter surprise, bewilderment, or astonishment. I was so taken aback when I found out I'd won the lottery that you could have knocked me down with a feather!
See also: could, down, feather, have, knock
Farlex Dictionary of Idioms.

you could have knocked me down with a feather

OLD-FASHIONED
If you say you could have knocked me down with a feather, you mean that you were extremely surprised by something. I won 54 votes to 48. You could have knocked me down with a feather!.
See also: could, down, feather, have, knock
Collins COBUILD Idioms Dictionary, 3rd ed.

you could have knocked me (or her, him, etc.) down with a feather

I (or she, he, etc.) was greatly surprised. informal
A similar idiom is found in Samuel Richardson's novel Pamela ( 1741 ) (‘you might have beat me down with a feather’); the modern form of the expression with knock dates from the mid 19th century.
See also: could, down, feather, have, knock
Farlex Partner Idioms Dictionary

you could have knocked me, etc. down with a ˈfeather

(informal) used to tell somebody about a very surprising experience: When they said how much the painting was worth, you could have knocked me down with a feather!
See also: could, down, feather, have, knock
Farlex Partner Idioms Dictionary
See also:
  • you could have knocked me, etc. down with a feather
  • take aback, to
  • I'll be damned
  • knock (one) on the floor
  • knock (one) on the ground
  • I'll be hanged
  • I'll be!
  • (well,) I'll be hanged!
  • (well,) I'll be!