Till is not a shortened form of until. Till has actually been in use longer than until.
They are often interchangeable; they both mean ‘up to’ (a point in time or event).
However, until is more likely to be used at the beginning of a sentence while till often appears before a noun. Until is also slightly more formal.
The contraction of until is ‘til and many sources will tell you not to use it. You can ignore them in informal contexts.
If I had a penny for every time I saw these mixed up, I would have a very heavy penny jar.
And I would get fed up of that face the cashiers at the bank pull when they see you are depositing lots of change.*
*I always sort it into the correct denominations and amounts, and put it into the little plastic bags. I don’t know why I still get the face.
‘Defiantly’ is not the only misspelling of ‘definitely’. However, it is the one that I read most often – spellcheckers don’t point it out with a helpful wiggly red line.
Definitely means without doubt or in a clear (definite) manner.
Defiantly means to do something in a way that shows resistance or rebellion.
As has previously been mentioned in the comment section of one of my posts, pore and pour are often confused. In my experience, this tends to manifest as writers using poured over when they actually mean pored over.
Therefore, I poured cream over the pudding and I pored over my latest manuscript.
Lightening is often used when the word should be lightning. It is a mistake that is easy to skim over when checking your own writing.
Lightning is a flash of light in the sky caused by electrical discharge. (It can also be used to mean fast and sudden.)
Lightening is the -ing form of lighten. Lighten has two meanings as a verb:
It is possible that some confusion arises because lighten can be used to mean to flash when referring to lightning (but I think this is rare).
Of course, this should be derring-do. But the misspelling is understandable given the meaning of the word and its origins.
Derring-do is pleasantly archaic and often used humorously in modern writing.* It means actions showing heroic courage or feats of daring.
The word originated from the late Middle English dorryng do (meaning ‘daring to do’) being misprinted as derrynge do in the 16th-century editions of John Lydgate’s Chronicle of Troy.
The modern usage and spelling is usually most associated with Sir Walter Scott’s Ivanhoe.
*I would love to proofread a story where derring-do doesn’t look out of place. I am imagining pirates. Or an old-fashioned superhero.
These two words have very different meanings. 
Often ‘grizzly’ is used when ‘grisly’ would be correct.
You could probably give your readers a little bit of an upset if you used ‘interred’ when you meant ‘interned’. Unless they really don’t like the character you are writing about – they might just be disappointed when they realise the mistake.
These are words to keep in mind if you tend to accidentally hit the wrong keys as you type – the spellchecker won’t object to them and the difference (n/r) is easy to skim over when you check your writing.
These two homophones are often confused.
This is my latest book recommendation. I consult this book regularly and it rarely lets me down. Respected and authoritative, it is a book with a sensible and measured approach to the English language.
The 7,500 entries are displayed in an A–Z fashion (like a dictionary, as per its name) with clear explanations and examples. It covers grammar, syntax, spelling, word choices and meanings, punctuation, and differences in English usage around the world. Fowler’s is my favourite source for identifying myths and ‘rules’ that are unnecessary and that damage good writing.
I referred to it in my previous post on ending a sentence with a preposition, and I have directed clients to it when discussing preferred forms of words. I even flick through it occasionally just to see what interesting entries I stumble across.
My hardback copy of the latest edition has 928 pages – you probably won’t want to carry it around with you! But it is an excellent publication to add to your collection. And (to my chagrin) it seems to be a lot cheaper to buy now than it was when I bought it.
Hannah McCall 