"Truth" implies "fundamental, firm, enduring" (PIE *deru-, "be firm, solid, steadfaast").
"Fundamental" is that which is found (Latin fundare, "to found" (i.e., foundation, base)).
So the phrase "fundamental truth" = steadfast foundation. This implies "Being in Time," Heidegger's project which was left uncompleted. Rather, later Heidegger moved to in-sight or poetic light.
This correlates with Godel's, von Neumann's, and Cohen's position of finding more in-sight by to framing a given system so that its covered or inexplicable t/f claims would become (be brought to) light.
For a mayfly, one day is what it knows, so almost all of its surround is fundamental truth...nothing much changes, in its lifetime's perspective.
A tortoise may live longer than a human, and so encounter fewer "fundamental truths" in its surround; however, the human being tends to be an historically-minded creature, and self-reflective, thus, even the Earth and Sun are understood to be non-fundamental truths; even the known Universe is believed to be non-enduring. The only fundamental truth may be the God of Abraham, etc.