The word "疾病" is formed by compounding two separate characters, each denoting illness. The character "疾" is composed of the radical "疒", representing sickness, combined with the phonetic component "矢" indicating its pronunciation, and historically connoting acute ailments. Similarly, "病" uses the same "疒" radical for meaning, with "丙" as its phonetic element, often associated with more severe or chronic conditions. Together, these characters combine semantically to create a broader term encompassing various diseases.