According to my dictionary, “propagate” means:
1 breed specimens of (a plant or animal) by natural processes from the parent stock: try propagating your own houseplants from cuttings. • [no object] (of a plant or animal) reproduce by natural processes: the plant propagates freely from stem cuttings. 2 spread and promote (an idea, theory, etc.) widely: the French propagated the idea that the English were violent and gluttonous drunkards. 3 (with reference to motion, light, sound, etc.) transmit or be transmitted in a particular direction or through a medium: [with object] : electromagnetic effects can be propagated at a finite velocity only through material substances | [no object] : a hydraulic fracture is generally expected to propagate in a vertical plane | (as adjective propagated) : a propagated electrical signal.
The first meaning applies to plants or animals, and the gloss only mentions that it doesn’t apply to plants. Odd that he doesn’t just say it has nothing to do with breeding, be it plants or animals. Since that’s very ambiguous — it could mean that it does apply to animals, or it could mean that he simply didn’t think about animals when he wrote the gloss — we are not served well by this definition.
I think it's obvious that the comment means "does not mean 'propagate' in the sense applied to plants" and not "can also mean to breed specimens but isn't applied to plants".
Considering that the main definition is "move through time toward the future", I take it that the idea is that {vIb} more generally means to move through any medium in the forward direction, but that it's so often used with time-travel that that's the assumed default unless context dictates otherwise. Speculatively, it hints that at the etymology of the word as having the broader meaning which narrowed as it propagated forward in time.
I would use it in a sentence like so:
{bIQDaq vIb 'otlhmey; cha' 'ujmey lID} "the photons propagated through two ujes of water".
(I wonder if {vIbHa'} could be used for "back-propagation" in the neural network sense.)
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