Yggdrasil is the great tree that sits at the centre of the Norse universe. its given etymology is Yggr (terror) a name for Odin/Woden and Drasil (steed). Taken literally we end up with it meaning Wodens Steed. This meaning evokes us to see the tree as a vessel for Wodens movements, something by which he travels the nine worlds. On a certain level this makes sense, but only on a very shallow level. For many reasons I struggle with this etymology and the given meaning, so below I will attempt to give alternatives/hidden options.
When breaking words down there are always many options, but here I will stick with two alternatives that I believe are both valid. first though we must break the word down, to Ygg-Dra-sil.
Now you may be thinking because this is a word still used today that it is invalid, but it is an old word and has the exact same spelling in Old Norse. You may also say well in Icelandic the G is pronounced K well this is also true, but if the double gg can be a K in egg why not Ygg or vice versa?. As for the vowel swap that is common occurrence and can be as simple as local dialect influence. Remember also that the spelling hides many words and as such is not meant to be exactly accurate. Also in Old English it is a homonym for Eye.
Now this is a proto Indo-European word, but we must consider not only the word but the age of the idea. From this root we get some interesting words. Yewg means to bind, unite, from it we get words like Yoke, something that is attached to animals (poetically linked to Burden). Also words like Yoga, unification of mind and body and yuga as in Kali Yuga meaning Age. Another note to add is its is essentially a homonym of an egg yolk via the word Yoke.
Draga is Old Norse for draw,drag and pull (carry), it has the shorter form dra (see Swedes ect) and in its Proto Germanic form its longer form is DragaN. It is related to the movement of a substance, but as you can see in its older forms becomes a homonym for Dragon.
Síl Old Norse for certain fish, mainly herring and in general fish young “fry”. We get words like old Welsh sil meaning small fish, all via the Proto-Germanic Síla. Interestingly we have an old Irish word Sil, from the Proto-Celtic Silom meaning seed, origin, semen and race (dependence).
Syll is an Icelandic word that in its current meaning means sleeper (railroad), but comes to us via the Proto-Germanic Sula, itself via the Proto Indo-European Sel both meaning bar or threshold, for instance the modern word windowsill.
Now we must add them back together to make sense of them. In the first meaning I will give it relates to Egg-dra-sil (above). This gives us a rather basic interpretation of conception (conceiving a child) we have the egg drawing the seed (which looks like small fry/fish young) . In a more general sense we have simply the conceiving (birth) of an idea, plan ect. Here Yggdrasil takes on a continual birthing process, a constant fertilisation.
When Woden/Odin hung himself from a tree for nine days ( 9 months?) he says, “Then I was fertilised and grew wise”. This helps us see the the tree in the sense of conception, Woden was born again and was given the runes.
The second meaning here, which I believe is related, would be via Yewg/yoke-dra-syll. This gives us “the yoke is dragging the threshold”. Added to this are the fact that yewg also gives yuga (age) we have “The drawing of the threshold of the age”. Again this gives us the idea of conception, this time though of an era,age or time. A constant pushing of the boundary of time, which is a good description of the present.
If we wished we could also mix it up a little and have the Yewg/yuga-dra-sil. Which gives us “the seed is drawing the age” or reverse it and use the homonym yolk-dra-syll, giving us “the yolk(egg) is at the threshold”.
I have grouped these two meanings together, because in a reduced sense they both give us conception, or a perpetual birthing. The birth appears to be within Yggdrasil, a sense it is in a constant motion of becoming, a perpetual conception. This is related to the Germanic concepts of time, we have no future tense in the Germanic languages, only present and past, the now being the constant conceiving, always striving. Yggdrasil via these ideas comes to literally mean the present, the now.