As already suggested in the works of those like Larissa & Giuliano Bonfante, the meaning of celu or cel as 'earth, ground' is well-founded. In more detail, we find calu in Old Etruscan and due to the regular raising of low a to mid e before resonants, the root eventually evolved to Late Etruscan cel(u)- which is why Liber Linteus shows locative forms like cel-i 'upon earth' (< *calv-i) and cel-θi 'in earth' (< *calv-i=θi). This word is usually however confused with the gloss Celius which was claimed centuries ago as a month in the Etruscan calendar.
Simultaneously, Indo-Europeanists have reconstructed a root *ḱel-/*kel- meaning 'to conceal, to hide' and since Indo-Europeanists seldom if ever dabble in the Etruscan language, as I hope to explain, there is a subtle logic conflict here. Ultimately I believe that this IE root may be yet another misidentification of a non-IE verb.
It's striking that Etruscan calu can so readily mean '(that which is) covered' by supposing an Etruscan verb root *cal- 'to cover' plus the transitive participle ending -u. This idle assumption isn't substantial in itself, of course, but it is when all direct evidence of the competing Indo-European root just so happens to be restricted to Europe.
The comparanda for PIE *ḱel-/*kel- has been from Germanic (*haljō- 'underworld' and *haljanan 'to hide') and Latin (cēlāre 'to conceal, hide, cover'). Some scholars will add Greek καλύπτω 'to cover, to hide' yet as Robert Beekes notes, the word is unanalysable in IE terms and shows a non-IE suffix *-u[p/b]- (cf. καλύβη 'hut, cabin'). It should also be asked why the Greek term should contain *a in its root. Some push a little too far, implicating "Indian šaras- 'skin over milk'" (which I'm having trouble verifying) in an apparent try to capitalize at once on r/l-alternation, satemization and shifting semantics to build an even flimsier house of cards. This strategy is far too easy and unconvincing. Adams and Mallory simply label it "WC" (West Central) which is a quiet way of admitting that the evidence is restricted to Europe and that they can't validate it as a genuine Indo-European root. All in all, while the root has become part of accepted Indo-European vocabulary, it nonetheless appears to be weakly justified.
This is where it may be wiser to look to Proto-Aegean to explain why the root is restricted to the west and why Etruscan looks in all appearance to be built on the so-called "Indo-European" root even though Etruscan isn't an Indo-European language. If we propose Proto-Aegean *kal- 'to cover over', then Greek καλύπτω and καλύβη is sourceable to a derivative *kalúpa. It's certainly better already compared to racking our brains wondering why the odd a-vocalism and suffix conflicts with IE grammar and with other identified cognate forms to the west. Likewise, the resultant Etrusco-Rhaetic transitive verb *kal can then explain the source of the Etruscan 'earth' word (perhaps also reflected in Rhaetic as χelθi 'in the earth'(?) in Schum SZ 12) while supplying a source for both Latin cēlāre and a Pre-Proto-Germanic *kal- whose initial plosive shifted to *h by Grimm's Law sometime after 1000 BCE. As with so many of these other curious Etrusco-Germanic correspondences, a language intermediary (Venetic *kal- ?) is plausible.
 Szemerényi, Scripta minora: Selected essays in Indo-European, Greek, and Latin, vol 63, part 4 (1991), p.2042 (see link).
 Mallory and Adams, The Oxford introduction to Proto-Indo-European and the Proto-Indo-European world (2006), p.492 (see link).