Someone who heard me interviewed on the radio wrote to ask:
Do you know the derivation of "sleeping in"? I know it means sleeping late, but why do people say "sleeping in" instead of "sleeping late"?
Short answer: "sleep in", in the meaning of "sleep late(r than normal)", seems to have developed as an idiom within the past 100 years, apparently borrowed from Scots. It's common in English for verbs in combination with intransitive prepositions — sometimes called "phrasal verbs" — to develop idiosyncratic uses and meanings, related in some metaphorical or analogical way to the meanings of the verbs and prepositions involved, but not entirely predictable from them.
The Oxford English dictionary puts "sleep in" under sense 1.g. of sleep, with two rather different meanings:
With in: To sleep in the house, or on the premises, where one is employed (contrasted with ‘to sleep out’); also Naut., to remain in one's berth all night; (orig. Sc.) to oversleep; also, to lie in (to lie in 4 at lie v.1 Phrasal verbs), to sleep late.
(7) to sleep in, to oversleep (Sc. 1881 A. Mackie Scotticisms 60). Gen.Sc.;
I suppose that the original idea of the "sleeping late" sense is that "in", meaning "in one's house" or "in one's bed", is opposed to "out", meaning "out in the world" or at least "out of bed". In addition to the OED's reference "to lie in", there's the verbal form "to stay in", and the noun "shut-in", with similar meanings of "in one's dwelling". The idea of being "in" rather than "out", associated with sleep, then takes on the extra connotation that one is staying "in" while sleeping during a period of time when one normally would be "out".
As this example illustrates, the existence and meanings of such Verb+IntransitivePreposition combinations in English are at best semi-regular.
Thus the meaning of over in sleep over is not the same as in oversleep, much less in start over, get over, or turn over. The up of "get up" is not exactly the same as the up of "give up", or the up of "show up". And although there's a regular pattern of completive up in combinations like break up, bust up, carve up, smash up, wreck up, this pattern doesn't extend to demolish up, destroy up, dissect up, fracture up. Similarly, we have wash up, freshen up, mop up, tidy up, etc., but not cleanse up, launder up, disinfect up, sterilize up, (For more about verbal idioms with up, see "A stubborn survival", 4/19/2004.)
Common meanings of verb+in combinations include
to cross a physical boundary into a designated space: break in, come in, go in, run in, walk in, wander in, etc.
to interrupt or join a process: break in (as to a conversation), butt in, chime in, join in, jump in, etc.
to cause something to be added to a designated set: add in, count in, throw in, toss in, etc.
to cause something to enter a desired initial state: break in (as an engine or a pair of shoes), burn in (as a computer chip), etc.
to fail to leave a designated space: stay in, sleep in, etc.
In some cases these are simply productive combinations of the forms and meanings of the words involved. Thus come in, walk in, etc., are paralleled by innumerable phrases with other directional adverbials substituted for "in": come home, walk home, or come to Philadelphia, walk to Philadelphia, etc. But break in (as in what a burglar does) doesn't correspond to *break home; join in doesn't work with other directional phrases substituted for "in", e.g. *join to the conversation. Combinations like "join in" (or "sleep in") are apparently quasi-idiomatic results of drift and analogy in the phrasal lexicon.
The "sleep late" sense of sleep in seems to be one of these quasi-idioms, whose entry into general usage is apparently fairly recent. The OED's citations include three from the 19th century with a clear Scottish connection:
1827 C. I. Johnstone Elizabeth de Bruce I. iii. 56 Ye whiles sleep in on a morning.
1883 W. Aitken Lays of Line 58 A'e mornin' last March, when Rab Black sleepit in.
1888 G. MacDonald Elect Lady 138, I had to be up early, and I was feared I would sleep-in.
The earliest incompletely-Scottish citations are from 1931:
1931 Amer. Speech 7 20 Sleep in, to sleep late. ‘I'm going to sleep in tomorrow.’
1931 D. L. Sayers Five Red Herrings i. 16 Shall I tell Mrs. McLeod to let you sleep in, as they say? And call you with a couple of aspirins on toast?
The semi-regular metaphorical extension of words for spatial relationships is a linguistic universal, as far as I know — it's certainly been ubiquitous in the history of the Indo-European languages.