못하다

Etymology
.

Verb

 * 1)  cannot (do); to be unable, or impossible (to do)
 * 2)  not be good at
 * 1)  not be good at

Usage notes
The second sense is very commonly confused with. The contrast is in fact solely orthographic, as there is no prosodic difference between the two and the adverb can have the sense of "poorly" with all verbs.