sill
After reading npmlog module source code (which is used by npm), I believe the word sill come from silly, which means the most detail log level in npm install process. There are 9 levels of log in npmlog: silent, error, warn, notice, http, timing, info, verbose, silly.
log.addLevel('silly', -Infinity, { inverse: true }, 'sill')
pacote
pacote is a module used by npm to download dependence packages metadata.