Ah, I see I should have read more closely.
I actually did some research that touches on this.
The ST- assonance (initial consonant cluster) has a long and varied and surprisingly coherent phonosemantic history, dating from a pre-Proto-Indo-European era.
I tripped over ST- while trying to figure out what style meant, in a paper on metaphors, for a literary journal named Style. As usual, there was a lot more stuff going on than I had expected.
The paper is called "Style Stands Still", and I see no reason to reproduce it here, since it's online. (The stuff about ST- starts on page 8, but it's built on the context of the first part; the paper is 20 pages long, with bibliography).
EDIT: By request, a brief excerpt from the paper:
Figure 1. st-initial PIE roots, with some reflexes in Modern English
Source: Watkins (2000), Pokorny (1959)
- *stā- ‘To stand, with derivatives meaning “place or thing that is standing”’ (Pok sta- 1004)
style, stand, steed, stud, stay, stage, stamen, standard, stem, station, stasis, static, status, stable, stoic, store, stylite, steer
- *steigh- ‘To stride, step, rise’ (Pok steigh- 1017)
stile, stirrup, stickle, distich, acrostic
- *steu- ‘To push, stick, knock, beat’ (Pok 2. steu- 1025)
stub, steeple, stoop, stutter, stock, stoke, steep
- *stel- ‘To put, stand; with derivatives referring to a standing object or place’ (Pok 3. stel- 1019)
stolon, stalk, stele, stilt, pedestal, stolid, stall, stout
- *ster- ‘Stiff’ (Pok 5. ster- 1029)
stare, starch, stork, starve, stark, stern, strut, start, stark, startle
- *stebh- ‘Post, stem; to support, place firmly on, fasten’ (Pok steb(h)- 1011)
stoop, staff, staple, stump, stamp, stomp, stave
- *steip- ‘To stick, compress’ (Pok steib(h)- 1015)
stubble, stiff, stipple
- *steg- ‘Pole, stick’ (Pok 2. (s)teg- 1014)
stake, stack, stagger
- *stegh- ‘To stick, prick; pointed’ (Pok stegh- 1014)
stair, stick, sting, stigma, stimulate, stag
There is a strong family resemblance among the roots here. Indeed, on perusing this list, one finds a persistent cognitive image building up, with at least the following four significant perceptual properties:
Figure 2. Cognitive semantic properties of st-initial PIE roots
- One-Dimensional: The image has only one salient major dimension
- Vertical: That dimension is situated in an up-and-down orientation
- Strong: The image displays rigidity, stability, and physical integrity
- Still: The image is either unmoving, or frozen in motion
...
Not all of the characteristics in Figure 2 will be true of every Modern English word that comes from the roots in Figure 1, but some combination of the features applies to them all. For instance, although the Modern English words stamen, stile, steeple, stalk, stork, staff, stake, and stick each come from a different PIE root, all of them refer either to long rigid objects or to things characterized by such, mostly vertically oriented, and often supporting, attached, or applied to other structures by their ends. For that matter, they tend to apply to any Modern English word beginning with st-, no matter where it comes from.
You pose what I take to be two questions:
(1) Why is 'head hair' two words instead of one (especially given other words like bedroom)?
We all know what a car radio, a toaster oven, a graveyard shift and a spring chicken are; I don't think we'd benefit from making them a single word, even if other languages might do so -- indeed French and German have 'autoradio' instead.
'Word count' is really about language-specific word derivation practices, practices that might be constrained by grammar or just by custom.
The more interesting question you pose is
(2) Why is there no separate lexeme for head hair?
Well, as others mentioned, there are rare words like 'chevelure' and 'coif' that may fit the bill; on the other hand, they might be better viewed as foreign words. In any case even without them I think we need to remember that vocabulary does not develop merely as a result of 'need': there is a lot of randomness in language (one might draw an analogy to 'genetic drift' in the theory of evolution, which results in random elimination of some genes in a population, merely as a result of chance (http://evolution.berkeley.edu/evosite/evo101/IIIDGeneticdrift.shtml)).
I personally think that English has a lot of vocabulary that is not 'needed' by any objective, non-sentimental criteria, since other languages seem to make do with paraphrase in the same situation (and likewise for other languages). Vocabulary seems to develop by random acts of creativity that are not especially 'useful' (slang is a perfect example, which lives and dies on sociological grounds, rather than on 'being unable to express oneself otherwise', although I accept the distinction between the two is not quite that clear-cut).
PS The word for 'gloves' in German is 'Handschuhe', or 'hand shoes'. No separate lexeme.
In brief, I think it is mostly because of chance that there is no separate lexeme for head hair.
Good evidence against this view would be evidence that, for example, discussion of head hair was taboo among prior English speakers (for example, because it invited the wrath of God. Many religions do still have hair taboos). A similar phenomenon is believed to have occurred for 'bear', which in many languages is derived from a circumlocution. In Croatian the word for 'bear' is literally 'honey-eater.' Even English's 'bear' is derived from 'brown.' The reasons are thought to have to do with warding off bad luck by avoiding a direct, separate name. See http://www.cloudline.org/LinguisticArchaeology.html.
But I know of no evidence for such a theory as regards head hair, nor even for the simpler theory that English speakers thought of head hair in a different way (a culture-determines-vocabulary type argument).
Best Answer
From the OED in relation to swallow (the bird):
I suspect the reference to the Old Teutonic swalwōn- by the OED, and its comment that the etymological meaning 'is disputed' might be a reference to Kluge's 1891 'An Etymological Dictionary of The German Language'.
Kluge has this to say:
Noting that ἅλκύων is Greek for halcyon, or kingfisher. All of this leaves me better informed, but none the wiser. There's more to be told about the pre-Teutonic roots perhaps and the link with that Greek word.