This is the 2534th most frequent Turkish word.
olmasa
"Olmasa" means "if not" or "if it does not exist/happen".
The word 'olmasa' in this sentence forms a conditional scenario about rain not occurring and the implications of that.
Eğer yağmur olmasa dışarı çıkabilirdik.
If it weren't raining, we could go outside.
Here, 'olmasa' is used to express a hypothetical condition of the absence of help and its impact.
Onun yardımı olmasa bu işe başlayamazdım.
If it weren't for his help, I couldn't have started this job.
In this case, 'olmasa' creates a conditional clause imagining a world without electricity.