Let me spell it out - What am I?

Question

Let me spell this out for you,
And see what you can do.
I begin by being half full,
Then onto you, don't be dull.
I'm around for a third of a year.
Finally, without me, there is no gear.
Let's see if you can puzzle how,
Ultimately the riddle's now,
Now ready for you to complete.
Granted, it might be elite.

Hint 1:

The answer is shorter than short.

Answer 1

The answer is staring everyone in the face.

Lung

Let me spell it out for you / And see what you can do

See end for explanation

I begin by being half full,

Half of "full" is "l".

Then onto you, don't be dull.

Onto "you", or "u".

I'm around for a third of a year.

Annual is used here. "nn" is 1/3 of "annual", so "n"

Finally, without me, there is no gear.

Can't have "gear" without "g"

Let's see if you can puzzle how,
Ultimately the riddle's now,
Now ready for you to complete.
Granted, it might be elite.

Take the first letters of each of the last four lines, and it's literally spelled out for you.

Answer 2

I think it's

COMPUTER.

Update: unfortunately this doesn't fit Hint 1. But with a little help from Aify, I've managed to make it fit everything else!

Let me spell this out for you,
And see what you can do.

This tells us that it's going to be a letter-building riddle.

I begin by being half full,

Half of the word "complete", a synonym of "full" (the OP does like his synonyms!) is COMP.

Then onto you, don't be dull.

The letter U sounds like "you", so add that to our word.

I'm around for a third of a year.

Credit to Aify for this part...

"Twelve months" is a synonym of "year", and one-third of its letters are T's and E's, so this gives us the letters TE.

Finally, without me, there is no gear.

The letter R is contained in the word "gear".

Let's see if you can puzzle how,
Ultimately the riddle's now,
Now ready for you to complete.
Granted, it might be elite.

This is probably a cheeky hint that the answer to the riddle is exactly what you're looking at right now!

Damn nice riddle by the way.

Answer 3

Here's a guess:

WAR

I begin by being half full, Then onto you, don't be dull.

The first letter is U+U = W, half of W is U.

I'm around for a third of a year.

If I'm using ANNUAL, the letter A composes 1/3 of it.

Finally, without me, there is no gear.

Without the letter R, you can't complete the word gear. Also might be referencing pop culture games, or the need for gear when at war.

Answer 4

ANALYSIS (And partial incomplete answer)

Let me spell this out for you and see what you can do.

I begin by being half full

FU (LL) - we use FU since having LL at the start of a word doesn't make sense. Option 2: we use the COMP part of "complete" since complete is a synonym for "full"

Then onto you, don't be dull

onto you likely means the letter "U", or it can be "on two u" signifying a second "U" in the word

I'm around for a third of a year

This is likely to be the synonym "annual" or "annum", but only "annual" divides nicely into thirds, so it could be either an, nu, or al. It can also be interpreted as "twelve months", which gives us several possibilities: 1) take a part of "twelve months" and use that; 2) the total number of T and E's make up a third of the phrase "twelve months"; 3) A third of twelve months is 4 months. Usage of the phrase "four" or "triannual" or "Quadrimestrical" or "quad" is possible.

Finally, without me, there is no gear

Either signifying one of the letters (G or R, likely) in gear - the other option here would be that if the hint was something to do with gears (either in a car, or in machines (cogs and gears)).

Taking into account the hint that the answer is shorter than "short", which is 5 letters, the answer should be 4 characters or less. This means that because there are 4 clues, it's likely that each clue represents a single letter.

First Letter:

Half full - half the letters in full are L's, so we start with the letter L.

Second Letter:

Onto you - Letter U

At this point we can start looking at this: http://www.wordhippo.com/what-is/starting-with/4-letter-words-lu.html

Third Letter:

year, aka annual - it's the third letter, so a third of a year makes sense, and we can take the A.

Final Letter:

Finally, without me, there is no gear - this one's a stretch, but the letter "u" isn't in gear. TBH can't really make sense of this one

Word:

Luau, a word for party. Why does this work? If you look at the line "Ultimately, the riddle's now", it bears a striking resemblance to "the party is now!" If we replace the word "riddle" with luau, it seems more like something we'd hear in modern language; "The luau (party) is now!"

Answer 5

New answer since my first one has been popular and fits everything except Hint 1.

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The hint tells us that we're looking for a word of 4 letters or less. Thus I think each of the 3rd, 4th, 5th, and 6th lines gives exactly one letter in the word.

Let me spell this out for you,
And see what you can do.

This tells us that it's going to be a letter-building riddle.

I begin by being half full,

The letter L forms half of the letters in the word "full".

Then onto you, don't be dull.

I'm still sticking with my interpretation of this line as U (which sounds like "you").

I'm around for a third of a year.

The word "season" can mean a year, e.g. the $n$th and $(n+1)$th seasons of a TV series are often separated by 1 year. One-third of the letters in this word are S.

Finally, without me, there is no gear.

I'm not sure on this line, but there aren't many 4-letter words beginning with LUS, so I'll go for T,

giving the final answer as

LUST.