Etymology tree
Proto-Germanic *warmaz
Proto-Indo-European *-yeti
Proto-Indo-European *-éyeti
Proto-Germanic *-janą
Proto-Germanic *warmijaną
Proto-West Germanic *warmijan
Old English wierman
Proto-West Germanic *warmōn
Old English wearmian
Middle English warmen
English warm
Proto-Indo-European *-yósder.
Proto-Italic *-āzios
Latin -āriusnom.
Latin -āriusbor.
Proto-Germanic *-ārijaz
Proto-West Germanic *-ārī
Old English -ere
Middle English -ere
English -er
English warmer
From warm + -er.
Meanings
Something that warms (something else) by providing some small amount of heat, such as a hot water bottle or a soup.
[…] tortillas are kept warm and moist in an electric warmer […] 1993, Raymond Sokolov, Why We Eat What We Eat:
A piece of clothing for warmth via insulation of body heat.
An introductory activity, for example in a lesson, to stimulate interest in a topic.