Unfortunately there is no list or series of meanings that can be attributed to a particular knot, according to archeological and anthropological findings. If you are going to use a design or knot for something personal, choose something that really appeals to you and that'll be the most accurate definition of all. Certain types of people or personalities will prefer spirals over knots for some reason, or animals over spirals, or whatever. This reflects better what the symbols mean that anything, given that the meanings used today are only romantic versions of what the Celts believed.
That said, people always ask for some mystical meaning behind Celtic art, so here are some of the published stuff that's out there. HOWEVER, keep in mind they are only romantic interpretations of any true meaning the ancient Celts may have held.
- the interconnection of life and humankind's place within the universe. Common knots include the Trinity knot, thought to represent the Holy Trinity or the Triple Gods/Goddesses of the ancient Celts; and the Lover's Knot, representing 2 together as one (resembles intertwined infinity symbols).
- usually reflects personal spirit, and an individual's attainment of balance in the inner conciousness and outer self. May also represent the cosmos, heavens, and water (waves). A common spiral type pattern would be the Triskel, thought to represent the Holy Trinity or the Triple Gods/Goddesses of the ancient Celts like the Trinity Knot (above).
- an individual's journey through life (as in through a labyrinth), their path of experiences and learning.
Lions - nobility, strength
Snakes - rebirth (Dragon or serpent designs may be interpreted the same as snakes)
Birds - purity (peacocks) or nobility (eagles)
Salmon - knowledge
Bull - strength
Boar - ferocity, strength
In Search of Meaning: Symbolism of Celtic Knotwork - by Stephen Walker