lastly vs sooner or later

lastly

adv
  • Used to signal that the speaker is about to yield control of the conversation. 

  • Used to mark the beginning of the last in a list of items or propositions. 

sooner or later

adv
  • Eventually, at some undetermined time in the not-too-distant future. 

How often have the words lastly and sooner or later occurred in a corpus of books? (source: Google Ngram Viewer )