thermal underwear
nounUK /ˈθɜː.məl ˈʌn.də.weə/
US /ˈθɝː.məl ˈʌn.dɚ.wer/
Warm clothes you wear under your other clothes to stay cozy in cold weather.
She put on her thermal underwear before going out to play in the snow.
OTHER MEANINGS
2. Clothing made of special fabric that keeps body heat in.
These thermal underwear pants are made of soft fleece.
3. A set of top and bottom worn for winter sports.
He packed his thermal underwear for the ski trip.
4. Extra warm underclothes worn by campers and hikers.
The hikers wore thermal underwear to stay warm at night.