What word is 咲かそう an inflection of?

Question

I saw this word in a song. The lyrics read:

大きな花を咲かそうとしてる

What word is it an inflection of? I can't figure it out.

Answer 1

「[咲]{さ}く」 ← Base verb. "to bloom"

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「咲かす」 ← Causative form of 「咲く」. "to let/make bloom"

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「咲かそう」 ← Volitional form of 「咲かす」. "willing/about to let/make bloom"

Thus, 「大きな花を咲かそうとしてる」 would mean:

"trying to make big flowers bloom" or

"~~ is about to make big flowers bloom"

At least one of these would fit the context. If neither one does, you will need to show more context.

Answer 2

It's an inflection of

咲く

Besides, its causative verb form is,

咲かす

If you transform the word ending with おう to make it volitional verb,

咲かそう

Your lyric can read as :

We are giving a try to bloom big flowers.

To add a knowledge, It has its sibling which works almost the same

咲かせる

Both of them works as a causative verb.