There is a lot of regional variation on the meanings of these words. I am only familiar with US English and UK English, others can fill in the blanks:
Jumper: In the UK this just refers to an garment you wear over your shirt for warmth. It doesn't have buttons, and it pulled over your head.
In the US this has a completely different meaning. It is a type of girl's dress, a top, with attached shorts basically. (Google will be happy to show you images.) It has a kind of "little girl" sense to it kind of like pinafore, however, for sure adult women wear them too.
Sweater: In the UK this is the same as a jumper, a garment you wear over your shirt, with no buttons, and is pulled over your head.
In the US this is a similar item, however, a cardigan with buttons can also be called a sweater in the US.
Pullover: again is a garment you wear over your shirt, pulled over your head. The meaning is the same in the US and UK, but it is a pretty uncommon word in the US.
So in the UK it all means pretty much the same, however there are considerable semantic variations in the US.
This is just based on my personal observation having lived in both countries. I am sure there are lots of subtle regional variations. For example, in the UK the further north you go, the more likely you are to use jumper instead of sweater, and vice versa. Though pullover is pretty universal.
When you use the word group your emphasis should be on the collection of things in the group.
How many people do you have in your group?
When you use the word grouping your emphasis should be on the act of forming the group rather than the group itself.
Which grouping would be better- girls in one group and guys in another, or else adults vs children?
Best Answer
Resiliency is just a variant of resilience. Which one is used is a matter of style and personal preference. I would always use resilience because it's one syllable shorter than resiliency. Others may have different opinions. It doesn't matter because they are, as you suggest, exact synonyms, except for the pretentiousness of the longer word: resiliency. All verbosity is pretentious.