I think of the word cupboard as an old fashioned term for cabinet.

I think of cabinet as the thing that is installed in the kitchen. I think of cupboard as a freestanding piece of furniture. But I also don't think those are necessarily definitional, just how I use the words.

Same thing. I use them interchangeably. But if I were to really break it down, I'd say a cupboard is one unit. A cabinet is multiple cupboards.

I think of a cabinet as a unit, a technical term describing the box. The storage area is generally a cupboard (comprised of multiple boxes). It's kinda old-fashioned and I think that's why I cling to it.

What ellendi said.

A cupboard is a place to store your dishes. A cabinet is just a fancy name for the cupboard to store your dishes, pots, pans, and stuff you hardly ever use or even need.

Cupboard is built in cabinet is furniture.

Or maybe its vise versa. Is anyone gonna look and give us the "proper" definition?

Not particularly controversial and their is no real decisive definition. I think of cupboard as what Mother Goose and Snow White use and cabinets what I have in the kitchen.

From WiseGeek:

In general, there are few true differences between a
cupboard and a cabinet. The two terms are almost synonymous, though some
people consider the difference between them to be the presence of
shelves within the unit: cupboards have shelves, while cabinets do not.
This is a loose distinction, however, and some people consider a more
accurate distinction to be the primary use of the item: cabinets are a
broad term for storage units, while cupboards are used specifically for
displaying cups, plates, and other flatware by using doors with glass
panes.

A cupboard and a cabinet can be a freestanding unit or a wall-mounted
unit, and very often no physical differences are apparent between the
two. Many people will label a cupboard as a cabinet with a wood and
glass door that allows a person to see into the unit to view the
contents; some cupboards even feature no doors at all, revealing the
plates and cups within. A cabinet can be more multi-purpose, and storing
items in a cabinet can be done with or without shelves. Pots and pans,
for example, are often stored in lower cabinets beneath a countertop.

Some freestanding units will combine a cupboard and a
cabinet. The higher cupboards may be used for display purposes, while
the lower cabinets can be used for storage of heavier items or less
attractive items that the owner does not want to show off. Kitchens also
often feature several wall-mounted cupboards as well as wall-mounted
cabinets for storage of different kitchen tools and cooking items.
Another distinction between cupboards and cabinets lies in this kitchen
configuration: some people contend that cupboards are used for storing
foods, while cabinets are used for storing cooking tools such as pots
and pans.

Regardless of the true distinction a cupboard and a cabinet will
serve generally the same purposes, and it is up to the owner to decide
how the cabinets or cupboards are used. Many people convert cupboards
and cabinets into spaces for storing dishwasher units, trash compactors,
and other common kitchen tools that can be otherwise unsightly. The
cupboards and cabinets are very often made from wood, but other types of
materials can be used; stainless steel is a popular choice for
durability and aesthetics, and composite materials have become more
popular for cost savings, durability, and resistance to water damage.

my family never used the word cupboard when I was growing up, nor did my friends... I knew the word from the 'old mother hubbard' rhyme...

but my husb grew up with that word and uses it for all cabinets in the kitchen-upper and lower... I assumed it's use was maybe regional- he grew up in the rural Midwest...

I grew up saying cupboards, but now say cabinets. I think cupboard is a more old-fashioned term, and is used regionally.