An Excerpt from My Recent Treatment of the Name Lancelot

... As it turns out, I don't believe any of that is relevant. Instead, to me at least, Lancelot looks like Chretien's attempted rendering of Late Latin

lancĕŏlātus, a, um, adj. [lanceola], armed with a little lance or point, lanceolated, lanceolate: plantago, Macer de Plantagine, 5.

Combined with the 'du Lac' title, I now feel fairly confident in identifying Lancelot (as I did in the past, without benefit of the bit on lanceolatus) with the Irish god Lugh, whose name in Welsh occurs as Llwch, the same spelling found for the word "lake":

llwch2 

[cf. e. lle Crn. Looe, H. Lyd. luh ‘llyn’, H. Lyd. lohan, gl. paluster, Llyd. Diw. lo(u)c’h: ?cf. H. Wydd. loch (> S. loch, lough)] 

eg. ll. llychau.

Llyn, pwll, merddwr, cors, mignen, siglen, gwern; llaid, budreddi, baw, tom, hefyd yn ffig.:

lake, pool, stagnant water, bog, swamp, marsh; mud, mire, grime, filth, dung, also fig. 

Lugh possessed the Gae Assail, a legendary spesr recognized as one of the Four Treasures of the Tuatha Dé Danann. His Welsh counterpart Lleu kills Goronwy Pebr with a spear, piercing through a stone slab to strike his enemy on the bank of the River Cynfael.

I suspect one of the epithets of Lugh contributed to Chretien's adoption of lanceolatus. 

We may begin with Llwch Llawwynnauc, which is probably a Welsh substitute for the Irish Lugh Lonnbemnech. This became Lluch or Lleawc Lleminauc in The Spoils of Annwn. And Lleminauc became Culhwch and Olwen’s Llenlleawc the Irishman.

Lugh Lonnbemnech >

Llwch Llawwynnauc >

Lluch/Lleawc Lleminauc >

(Lluch/Lleawc) Llenlleog

Common copying errors often substituted certain letters for each other, and we can easily imagine a form of an epithet whose first element was mistakenly related to W. llain -

llain 

[?bnth. H. Wydd. láigen ‘gwaywffon flaenlydan’; ymddengys mai deus. oedd y gair yn wr. yn ôl tystiolaeth yr enghrau. cynharaf] 

eb.g. ll. lleiniau, lleinau, (prin) lleini.

a Llafn, cleddyf, gwayw, gwaywffon:

• blade, sword, spear. 

- and whose second element was taken as the standard Welsh diminutive suffix -awc. This is especially true given the god's spear attribute.

If I'm right, then Lancelot of the Lake is Lugh of the Little Lance (which has rather unfortunate Freudian overtones!).