Definition of subtilty in US English:

subtilty

noun

  • 1A refinement of thought or argument; a fine point; = "subtlety". Usually in plural.

  • 2Refinement in argument or speculation; (excessive) use of fine distinctions.

  • 3Cookery. = "subtlety". historical after 16th cent.

Usage

Now rare (chiefly superseded by subtlety)

Origin

Late Middle English (in an earlier sense). Partly an alteration of subtlety after subtile, and partly a variant of subtility with reduction of the final syllable.