It also has a few less commonly used meanings, as Elizabeth has pointed out.

1. a person easily cheated, deceived, or imposed upon.

(a person who is gullible and easy to take advantage of)

Origin:

Traces the meaning to the fish called a sucker, on the notion of being easy to catch.

2. a person attracted to something as indicated:

“He’s a sucker for new clothes.”

3. Slang. any person or thing:

“He’s one of those smart, handsome suckers everybody likes.”

“They’re good boots, but the suckers pinch my feet.”

2 : a shoot from the roots or lower part of the stem of a plant

3 : any of numerous chiefly North American freshwater bony fishes (family Catostomidae) closely related to the carps but distinguished from them especially by the structure of the mouth which usually has thick soft lips — compare HOG SUCKER, WHITE SUCKER

4 : LOLLIPOP 1

5 a : a person easily cheated or deceived b : a person irresistibly attracted by something specified c — used as a generalized term of reference