sitting idle vs. sitting idly

[virus99]

Good morning forum!

This is a quote from Cambridge D. Online:

It's crazy to have £7000 sitting idle in the bank.

I wonder why we do not say "sitting idly" in the bank, as idle describes the verb sitting. Or is it just an added adjective - must be when it's no adverb .
Is the following sentence valid then:

It's crazy to have £7000 idle in the bank.

Adverbs and adjectives are one of my favourite topics ( sigh).

Thanks in advance!

[BobK]

'Idly' would conjure up a rather surreal image of the cash sitting around, twiddling its thumbs, and saying 'I hate Sundays'!

Compare

'I will not stand idly by while they do this to you'. ('Idly' is an adverb of manner.)

Your cash is just 'idle' (an adjective).

b

[virus99]

Thanks Bob.

No worries, my own money has better manners (at least I hope so).

It's crazy to have £7000 idle in the bank.

Is that sentence valid? Thanks again.

[emsr2d2]

Thanks Bob.

No worries, my own money has better manners (at least I hope so).

It's crazy to have £7000 idle in the bank.

Is that sentence valid? Thanks again.

I would be very happy to have £7000 in the bank, idle or otherwise!