The story
- Proto-Indo-European*leh₁-
- Proto-Indo-European*leh₁d-
- Proto-Germanic*lataz
- Proto-West Germanic*lat
- Old Englishlæt
- Old Englishlatost
- Middle Englishlaste
- Englishlast
- Proto-Germanic*dīkaz
- Proto-West Germanic*dīk
- Old Englishdīċ
- Middle Englishdich
- Englishditch
- English todaylast-ditch
From last (adjective) + ditch (noun), referring to an innermost military entrenchment which acts as the last line of defence.
Etymology from Wiktionary, CC BY-SA 4.0.