IPA: /θwɔːrtər/
KK: /θwɔrtər/
A person or thing that prevents something from happening or stops someone from achieving their goals.
The hero was seen as a thwarter of evil plans.
Thwarter is derived from the verb 'thwart' (from Old English 'þwartan', meaning to turn aside or oppose) with the suffix '-er' (meaning a person who). Thus, a 'thwarter' is a person who turns aside or opposes something.
Think of someone who 'turns aside' ('thwart') an action or plan — that's why a thwarter is someone who opposes or prevents something.