IPA: /ˈθɜːrməli/
KK: /ˈθɜrməli/
In a way that relates to heat or temperature.
The materials were tested thermally to ensure they could withstand high temperatures.
Thermally → It is formed from "therma" (from Greek "thermos", meaning heat) and the suffix "-ly" (meaning in a manner). The word "thermally" refers to something done in a manner related to heat.
Think of 'heat' ('thermos') to remember that 'thermally' means in a manner related to heat.