1. (Science: botany) a bud.
2. A precious stone of any kind, as the ruby, emerald, topaz, sapphire, beryl, spinel, etc, especially when cut and polished for ornament; a jewel.
3. Anything of small size, or expressed within brief limits, which is regarded as a gem on account of its beauty or value, as a small picture, a verse of poetry, a witty or wise saying. Artificial gem, an imitation of a gem, made of glass coloured with metallic oxide.
4. (Science: prefix) Prefix denoting twin substitutions on a single atom; e.g., the gem-dimethyl substitution on carbon-4 of lanosterol.
Origin: shortened form of L. Geminus, twin; oe. Gemme precious stone, f. Gemme, fr. L. Gemma a precious stone, bud.