plimsoll

Short definition from Wiktionary

Noun

1. 1
   A rubber-soled lace-up canvas shoe for sports or onboard ships; a precursor of trainers.
2. 2
   The plimsoll symbol ⦵ (or o) that is used as a superscript in the notation of thermodynamics to indicate an arbitrarily chosen non-zero reference point.

Proper noun

1. 1
   A surname.