Learn English – the difference between “electric” and “electrical” and their usage

Partially is mostly used in contexts involving non-tangible description of things.

Example:

Your views are partially correct.

Whereeas partly is preferred for tangible description.

Example:

The construction is partly built on stone.

Moreover, 'partially' is more abstract and concrete w.r.t usage than that of 'partly'.

Try to think of it this way:

Specific and concretely describing

'half of the liquid' partly goes more with this.

Vague and non specific description

'Some of the liquid' partially is more apt here.

Generally, to attenuate is to dilute[1], and to extenuate is to excuse. While one sense of extenuate is "To make thin or slender; to draw out so as to lessen the thickness," the sense "To lessen; to palliate; to lessen or weaken the force of; to diminish the conception of, as crime, guilt, faults, ills, accusations, etc." is rather more commonly used.

[1] From wikipedia: "Attenuation is the gradual loss in intensity of any kind of flux through a medium." From wiktionary: "To reduce in size, force, value, amount, or degree; ... To weaken; ... To rarefy."

(I see that instead of "rarefy" being an alternative spelling of "rarify", wiktionary says it's the other way around.)

Note, many english.stackexchange denizens regard questions like the above (which is easily answered via websites like wiktionary) as unsuitable questions.