xia4 is a complex character whose origin is not clear. Some etymologists surmise that it is a graphical representation of an insect found in summer time, while others assert that it represents 'exposure of the face, hands and feet' due to the heat.
yan2xia4 means 'extremely hot summer'.
yan2 consists of two huo3 which means 'fire' so that 'fire on fire' indicates scorching heat. Another meaning of yan2 is 'inflammation'.
xia4ji4 means 'summer season'
has two components .
The first component is he meaning 'grain' or 'grain stalk'
and the second component is the character zi meaning 'son'
(an infant with arms stretched out). 'Young grain stalk that needed greater
care' was the original meaning but it was later extended to mean 'youngest
brother' and then the 'last month of the season' and finally arrived at
its present usage as 'season'.