An act of sucking.
"The baby spent most of the afternoon happily sucking on his pacifier while I tried to work."
In plain English: Sucking is a noun that refers to the act of drawing liquid into your mouth using a vacuum created by your lips and tongue.
"The movie had a reputation for sucking, so nobody wanted to watch it."
present participle of suck
"The toddler was sucking on his pacifier while watching cartoons."
In plain English: To suck is to draw liquid or air into your mouth by making a vacuum with your lips and tongue.
"The baby was sucking on her thumb while she waited for dinner."
Still nourished by the mother's milk, as an infant; suckling.
"The toddler refused to take a bite of his vegetables because he was still sucking at the breast during lunch."
In plain English: Sucking means being really bad at something or not working well at all.
"The sucking sound of rain hitting the roof was very loud."
Usage: Use this adjective to describe infants who are still nursing from their mothers rather than eating solid food. It specifically refers to babies in a state of being breastfed or bottle-fed during early infancy.
Derived from Old English succan, this verb originally meant to draw liquid into the mouth through suction. It retains that core sense of drawing in fluid or air while also extending metaphorically to mean deriving benefit from someone else.