Both words have multiple meanings, but the meanings which are synonymous would be:
light: weighing very little, or less than average.
slight: small in degree; inconsiderable.
Light is therefore a reference to weight, whereas slight refers to size, or mass. Obviously, an object's mass and weight are very different things.
When said about a person, "slight"...
I think Duke's answer covers much of the important distinctions.
It is hard to find a difference between them based on definitions.
From Merriam-Webster -
a person who sells things especially on the street
a business that sells a particular type of product
From Cambridge -
someone who is selling something: For the past few months she's been ...
Essentially both seller and vendor mean the same thing. Vendor is of French/Latin etymology while seller is from Old English.
Though with such duplicates we do love to look for shades of difference in tone or feel that even native speakers might argue over. You wouldn't really ever be wrong to just use seller and stick with it.
Given that caveat, if ...
The two words are mostly synonyms, but not entirely.
Target can refer to both:
the desired outcome of a plan or wish;
the physical spot which is supposed to be hit by a projectile (the bullet from a gun, the arrow from a bow...).
On the other hand, aim can be used only with plans ans wishes.
Please note that the above comments refer to the meanings of ...
I have found out that the use of both can mean "examine carefully" (as a doctor does in a health check or as your family do when they meet your boyfriend for the first time, in a more figurative sense).
I had a chance to poke and prod the SUV model, and drive the sport truck.
I've been poked and prodded by most of your family now.
He examined me silently, ...
It is also worth noting that "wealthy" is a much politer way of saying that someone has a lot of money than "rich" is. Often, this is a topic that should be talked about with some caution.
So for example:
He is rich! > There is a slight air of disgust/jealousy perhaps; I am showing my opinion towards the fact that this person has a lot of money and it is ...
In the UK we use '(in or to) the sum of' more than 'in the amount of'. For example on bank notes it says "I promise to pay the bearer the sum of" and I have seen cheques (yes that's British spelling!) with 'The sum of' printed on them.
So in your example you might say
I spent the sum of £100 out of my own pocket
However, certainly in speech it's now ...