subtler / sutler 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. 👇
subtler: (adjective) able to make fine distinctions.
sutler: (noun) a supplier of victuals or supplies to an army.
subtler: s·AH·t·ah·l·er
sutler: NA
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)