Used to introduce the object being compared to the subject, meaning "than" or "compared with".

To be extremely difficult; usually used in the phrase 比登天还难 bǐ​dēng​tiān​hái​nán, meaning "harder than reaching heaven"

even more; still more; used with 比 bǐ to show an increased degree when comparing things

difficult; hard to do; troublesome; not easy; problematic; the opposite of 容易 róng​yì