Meaning

adverb to a degree exceeding normal or proper limits

adverb in addition

originFrom Middle English to (“also, in addition to”), from Old English tō (“furthermore, also, besides”), adverbial use of preposition tō (“to, into”). The sense of "in addition, also" deriving from the original meaning of "apart, separately" (compare Old English prefix tō- (“apart”)). Doublet of to; see there for more.

Etymology from Wiktionary, CC BY-SA 3.0