fund

The root fund goes back to Latin fundus — "the bottom" of something: the bottom of a cup, the bed of the sea, the floor of a valley, and by extension the base or foundation a thing rests on. From fundus the Romans built the verb fundāre, "to lay a bottom under" — to found, to establish on solid ground.

That single image of "the bottom" splits English into two big branches.

The first branch stays physical and structural — the literal base under a building, and the abstract base under an idea:

- foundation — the bottom a structure is built on; later also the founding of an institution and the endowed body itself.
- found / founder — to lay the bottom of an organization (found a company); the person who does it (the founder).
- fundamental — belonging to the bottom; the deepest, load-bearing principle without which the rest collapses.
- profound — pro- (forward, toward) + fundus (bottom) = "reaching toward the bottom." First used of physically deep water and wounds, then of deep thought and feeling: a profound silence, a profound idea.
- unfounded — not given a bottom; a claim with no base of fact under it.

The second branch is purely financial. A fund is the "bottom stock" of money you keep in reserve — your base capital. From there:

- funding / funder — the money supplied, and the one supplying it.
- refund — re- (back) + fund = pour the money back to its base.
- underfunded / self-funded / government-funded — modern compounds about where the money base comes from.

The through-line never changes: fund/found is always "the bottom" — sometimes the concrete or conceptual ground a thing stands on, sometimes the reserve of money a venture stands on.

One warning about look-alikes. The found in "I found my keys" is the past tense of find — Germanic, nothing to do with fundus. And confound comes from a different Latin verb, fundere "to pour" (con- + fundere = "pour together," hence to blur and confuse) — same first three letters, but the "pour" family (fuse, confuse, infuse) is a cousin, not this "bottom" family.