Heard on some radio show on KQED as I was drifting off to sleep last night, the adverb underfeet (instead of underfoot). The original example is lost to me, but others are easy to find. The semantic motivation for this variant is clear — we have two feet for things to be under — so I thought the variant was likely to be a recent reshaping of the P + N compound to fit the meaning (roughly parallel to plurals in the first N of N + N compounds, in things like movies update, campuses information, and games hardware — some discussion here).
But underfeet turns out to be a venerable variant, even if it’s not recognized in any except the largest dictionaries.
A few cites. First, two literal ones:
Sierra Trading Post: New Balance 809 Trail Running Shoes – Cushion (For Women) [from a customer] “this shoe is heavy. However, you don’t feel the rocks underfeet. It is not a good mud shoe.” (link)
With burning sand underfeet, and scorching rays of the sun from above, blood dried up in the body, the brain became inflamed, followed by delirium, coma, death. (from The Story of the Great War, ed. by Francis J. Reynolds, Allen L. Churchill and Francis Trevelyan Miller, p. 421)
Then, two figurative ones:
I hated having my little brothers and sisters underfeet when I was that age, I just wanted to be left alone to read my books. (link)
I know that a lot of people’s pet peeve is the child wandering around in a restaurant. I’ve heard from former wait staff that children underfeet can be a hazard. (link)
Background: the OED entry for under foot | underˈfoot, adv. (not yet fully updated; first publ. 1921) has two relevant subentries:
Beneath the foot or feet; on the ground [cites from the 13th century on; at first separated, later hyphenated, eventually always solid]
Of a person or persons: about one’s feet, constantly (and irritatingly) present; ‘in the way’. colloq.
For the latter, here are all the cites:
1891 Harper’s Mag. June 62/1 He muttered something about children being underfoot and staring at such times.
1922 S. Lewis Babbitt xviii. 230 Kenneth Escott and she were always under foot.
1959 M. Scott White Elephant i. 3 It has been a trying month for her too, with Deryk always underfoot.
1981 ‘S. Woods’ Dearest Enemy i. 38 It’s really too much of a nuisance having him always underfoot when I’m trying to prepare my own meals.
(You’ll see that this subentry has in fact been updated since 1921.)
The OED gives underfeet as a variant form. All of its cites:
1539 Bible (Great) Isa. xiv. 19 As a dead coarse that is troden vnder fete.
a1630 F. Moryson in Shakespeare’s Europe (1903) v. vi. 496 The Empire..of the Greekes..hath beene vtterly abolished, and the people haue beene troden vnderfeete.
1641 J. Burroughes Sions Joy 33 They sought to cast shame upon the Saints,..trampling them underfeete as dirt.
1760 Impostors Detected I. ii. ii. 170 Sacred relicks trampled under feet!
1857 J. G. Holland Bay-path xxix, Her memory..trodden under feet by malice, prejudice, and superstition.
These examples could be interpreted as having a PP (= P + N) adverbial, though the solidified spellings from the 17th century suggest that the combination was at least sometimes thought of as a compound word, and the OED‘s editors clearly interpreted all these examples as having a compound Adv word, a variant of underfoot. And that’s what’s going on in the more recent examples.
I doubt that I’ll take up underfeet in my own speech — it still sounds odd to me, like some (but by no means all) of the Npl + N compounds — but it’s certainly been out there for some time.