Stipendium tam magnum grave auditu est.

Yes. Stipendium is a neuter singular noun, and in neuter nouns the nominative and accusative singular often look the same.

So stipendium can be either nominative or accusative in form, but here it is the subject because:

• it is the thing being described,
• it goes with est,
• and the adjectives magnum and grave both agree with it.

So the sentence structure is basically:

• stipendium tam magnum = the subject
• grave auditu est = what is being said about it

Because magnum modifies stipendium, and Latin adjectives must agree with the noun they describe in:

• gender
• number
• case

Since stipendium is neuter singular nominative here, magnum must also be neuter singular nominative.

So tam magnum stipendium or stipendium tam magnum means so large a salary or a salary so large.

Because grave is the neuter nominative singular form of the adjective gravis, grave.

The forms are:

• masculine/feminine nominative singular: gravis
• neuter nominative singular: grave

Since grave refers to stipendium, which is neuter singular, grave is the correct form.

Because Latin is using an adjective, not an adverb.

Here grave is a predicate adjective with est. In other words, the sentence says that the salary is grave in a certain respect.

So the pattern is:

• stipendium ... grave est = the salary is serious / grievous / painful
• auditu explains in what respect: to hear

If Latin used graviter, that would be an adverb, and the sentence would be built differently.

Tam means so and modifies the adjective magnum.

So:

• magnum = large
• tam magnum = so large

It is an adverb of degree. English can express this as either:

• so large a salary
• a salary so large

Latin often uses tam this way with adjectives and adverbs.

Auditu is the supine in -u of audio.

This is a special verbal form used mostly with certain adjectives. In this construction it means something like:

• in respect to hearing
• more naturally in English, to hear

So grave auditu means grievous to hear or painful to hear.

A learner does not need to think of auditu as an ordinary noun form in the sentence. The important point is that it is a standard Latin way of saying to hear after certain adjectives.

Because this is an idiomatic Latin construction.

English usually uses an infinitive:

• hard to hear
• painful to hear

Latin often uses the supine in -u after adjectives like:

• gravis
• difficilis
• facilis
• mirabilis
• horribilis

So instead of an infinitive, Latin can say things like:

• mirabile dictu = wonderful to say
• horribile visu = horrible to see
• grave auditu = painful to hear

So auditu is not random; it belongs to a recognized pattern.

They form a unit of sense.

• grave gives the judgment: serious, harsh, painful, grievous
• auditu gives the respect in which that judgment applies: to hear

So the idea is:

• grave auditu est = it is grievous to hear

Very literally, you could think of it as:

• it is grave in hearing

But natural English usually prefers to hear.

It looks similar to an ablative form, and historically it is related to old case forms, but in standard grammar it is usually called the supine in -u.

For most learners, the safest approach is:

• call it the supine in -u
• recognize that it is used after adjectives
• translate it as to hear or in hearing

That will help you read the sentence correctly without getting stuck in historical grammar.

Because Latin word order is flexible.

This order does a few natural things:

• stipendium comes first as the topic
• tam magnum stays close to it and emphasizes its size
• grave auditu gives the judgment
• est comes at the end, which is very common in Latin

Latin could also rearrange the sentence without changing the basic meaning much, for example:

• Tam magnum stipendium grave auditu est

So the order here is normal Latin style, not something you should force into rigid English order.