Can't determine the nature of こう in this sentence

Question

Here's the quote :

「三人で手をつないでこうね。」

The context is "three frogs are taking hands and are ready to go for a walk".

At first I thought こう here meant "let's go" but that would be いこう right?

The other possibility could be the adverb こう (more often そう) in which case it'd mean "they took each other's hands and like that [they went for a walk]" implicitly referring to the verb in the previous sentence.
I've never seen this grammatical construct before.

Therefore I am not sure what's the precise meaning here, plus it's quite an old book I guess so It could also be an expression that is not used anymore. What do you think?

Answer 1

It is a colloquial contraction of いこう, only found in the form of verb + いこう → verb + こう (so not in a place of a stand alone 行こう, as far as I know). It can also be こー or just こ. As far as a colloquialism goes, it's more of a childish one than a slang-ish one.

An old song (1998) by Puffy has this line:

車で　駆けてこ

It is a contraction of 車で駆けていこう. (The song is called 渚にまつわるエトセトラ.)

As a more recent example, I found this pattern used in a PR phrase (2020):

「鮮度のオイル、かけてこー」

The last part is a contraction of かけていこう.