varma

If you want one word to demonstrate what Esperanto's affixes actually buy you, this is it. Varma alone yields malvarma cold, varmega hot, varmeta lukewarm, varmigi to heat something, varmiĝi to warm up by itself, varmeco warmth as a quality, and varmo warmth as a thing. Seven words, one root, no memorisation. The figurative sense carries too - varma akcepto is a warm welcome exactly as in English - and varme does duty for warmly in both the physical and the friendly sense.