busy (adj.)youdaoicibaDictYouDict[busy 词源字典]
Old English bisig "careful, anxious," later "continually employed or occupied," cognate with Old Dutch bezich, Low German besig; no known connection with any other Germanic or Indo-European language. Still pronounced as in Middle English, but for some unclear reason the spelling shifted to -u- in 15c.

The notion of "anxiousness" has drained from the word since Middle English. Often in a bad sense in early Modern English, "prying, meddlesome" (preserved in busybody). The word was a euphemism for "sexually active" in 17c. Of telephone lines, 1893. Of display work, "excessively detailed, visually cluttered," 1903.[busy etymology, busy origin, 英语词源]
clutter (v.)youdaoicibaDictYouDict
1550s, "to collect in heaps," variant of clotern "to form clots, to heap on" (c. 1400); related to clot (n.). Sense of "to litter" is first recorded 1660s. Related: Cluttered; cluttering.