ton / tonne / tun are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
ton: NA
tonne: NA
tun: (noun) a large cask especially one holding a volume equivalent to 2 butts or 252 gals.
ton: t·AH·n
tonne: t·AH·n
tun: NA
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)