This is the 6460th most frequent Korean word.
없었을
A conjugated form of "없다," meaning "did not exist" or "there was not."
The word '없었을' indicates a past conditional state of 'not having' referring to the noun 'time'.
그는 시간이 없었을 때 일을 하지 못했다.
He couldn't work when he didn't have time.
Here '없었을' indicates a past condition of 'not having' related to the noun 'money'.
내가 돈이 없었을 당시에는 힘들었어요.
When I didn't have money, it was tough.
In this sentence, '없었을' describes 'not having' rain in a past conditional sense tied to 'summer'.