Gaja can mean the following:
1. Elephant (of which there are 8 types recognized in Sanskrit)
2. Hence, the number 8
3. A measure of length (a sum of 8 units)
4. A musical measurement
5. A foundation of earth upon which a house is built
Essentially it means “elephant” the other meanings are derived from that essential meaning.
Kesari can mean (assuming that the spelling is keza in Harvard-Kyoto Sanskrit transliteration):
Essentially it means “hair.” A lion has a mane, so it can be referred to as a kezari.
If the spelling is not kezari but kesari, the meanings are:
1. Same meanings of Hair / Mane / Etc.
4. Filaments of plants
Essentially it means Saffron – which has a color similar to sulfates and gold, and is produced from the pollen in plant filaments.
Now, this yoga – Gaja-Kesari – is formed by Jupiter. Jupiter’s color is saffron. Therefore the main meaning of the term Gaja-Kesari in astrology is:
– A mound of saffron.
Saffron is a color of religious significance – so the “mound of saffron” suggests the traits of Jupiter become ample: morality, philosophy, charity, learning, etc.
Other possible meanings, “golden elephant,” “heap of gold”, are also useful as images to evoke the prosperity caused by the Gaja Keshari yoga.
Others, “Elephant-lion” or “hairy elephant” are not very useful! :)