somewhat adv.

Middle English som, "someone, somebody, a certain person; a certain indefinite portion of something, some part," from Old English sum "some, a, a certain one, something, a certain quantity; a certain indefinite number" (as in some say). This is from Proto-Germanic *sumaz (source also of Old Saxon, Old Frisian, Old High German sum, Old Norse sumr, Gothic sums), from a suffixed form of PIE root *sem- (1) "one; as one, together with."

The word has had greater currency in English than in the other Teutonic languages, in some of which it is now restricted to dialect use, or represented only by derivatives or compounds .... [OED]

For substitution of -o- for -u-, see come. As a pronoun from c. 1100, "a certain quantity or number." A possessive form is attested from 1560s but remains rare. Use as a quasi-adverb before numerals began in Old English, originally "out of" (as in sum feowra "one of four").

The sense of "in some degree, to some extent" is American English, by 1745. The meaning "remarkable, quite a" is attested from 1808, American English colloquial.

Many combination forms (somewhat, sometime, somewhere) were in Middle English but often written as two words before 17-19c. Somewhen is rare and since 19c. used almost exclusively in combination with the more common compounds; somewho "someone" is attested from late 14c. but did not endure. Somewhy appeared occasionally in 19c. Scott (1816) has somegate "somewhere, in some way, somehow," and somekins or somskinnes "some kind of a" is recorded from c. 1200.

Get some "have sexual intercourse" is attested 1899 in an anecdote of Abe Lincoln from c. 1840.

Old English hwæt, referring to things in abstraction; also "why, wherefore; indeed, surely, truly," from Proto-Germanic pronoun *hwat (source also of Old Saxon hwat, Old Norse hvat, Danish hvad, Old Frisian hwet, Dutch wat, Old High German hwaz, German was, Gothic hva "what"), from PIE *kwod, neuter singular of *kwos "who," from PIE root *kwo-, stem of relative and interrogative pronouns. Corresponding to Latin quid.

Meaning "what did you say?" is recorded from c. 1300. As an adjective and adverb, in Old English. As a conjunction in late Old English. Exclamatory use was in Old English. What the _____ (devil, etc.) as an exclamation of surprise is from late 14c. As an interrogative expletive at the end of sentences from 1891; common in affected British speech. Or what as an alternative end to a question is first attested 1766. What have you "anything else one can think of" is from 1925. What's up? "what is happening?" first recorded 1881.

"To give one what for is to respond to his remonstrant what for? by further assault" [Weekley]. The phrase is attested from 1873; what for? as introducing a question is from 1760. To know what is what is from c. 1400; I'll tell you what to emphasize what is about to be said is in Shakespeare.

"to some degree (usually smaller or lesser), some degree or amount of, somewhat," Middle English som-del, obsolete in Modern English or reverting to two words, but very common in Old English as sume dæle "some portion; somewhat," probably adverbial use of a noun phrase, from some + deal (n.1).