i-adjective
Describes a person who is slow-witted, dim, or not sharp mentally. Often used in casual, mildly derogatory contexts.
あいつはとろいから、説明してもわからないよ。
He's so thickheaded that he won't get it even if you explain.
i-adjective
Refers to slow movement, reaction, or progress. Can apply to people, actions, or processes.
彼は仕事がとろい。
He is slow at his work.
このパソコン、動きがとろいな。
This computer is sluggish.