What part of speech is smouldering?

"Smouldering" can be either a verb or an adjective, depending on its use in a sentence.

Verb: When describing the act of burning slowly without a flame, such as "The fire smoldered in the ashes."

Adjective: When describing something that is burning slowly and without a flame, or something that is showing suppressed anger or passion, such as "He gave her a smouldering look" or "There was a smouldering resentment in his voice."