English
resistless
From resist + -less.
A compound of resist + -less
Proto-Indo-European *steh₂- ‘stand’
…
Latin sistō ‘cause to stand’
Latin resistere
Middle French resister ‘to resist’
Middle English resisten ‘to resist’
English resist
Today it means
adj That cannot be resisted; irresistible.
Language periods are conventional ranges, not dates for this word.
Etymograph / resistless