魁 is a bound morpheme (b.f.), meaning it never appears as an independent word in modern Chinese. It carries two main semantic families: 'chief, preeminent, first in rank' (as in 魁首 'chief, leader') and 'of imposing stature, stalwart' (as in 魁梧 'tall and strong'). It also has a specific cultural reference in 魁星, the god of literature in Chinese mythology. You will encounter it only inside compound words.