sort of thing, so, if so, in that case, well
然 centers on a state or condition being just as it is: something being so, a sort of thing, or a natural consequence. Its uses as 'if so' or 'in that case' follow from that same idea of things being as they are.
然 originally combined 灬 (fire) with 肰 (a phonetic component related to burning or roasting), and later came to express the abstract idea of 'so' or 'thus' through phonetic loan. The modern form retains 灬 at the bottom, but the upper part has been simplified and its exact historical development is uncertain.
The fire 灬 at the bottom suggests something burning or cooking, and the upper part looks like a dog 犬 and moon 夕. Imagine a dog roasting meat under the moonlight, and when it's done, you say 'just so' — it's exactly the sort of thing you expected.
For ゼン, picture a Zen master calmly accepting things as they are: Zen -> ゼン, and the master says 'so it is' while sitting by the fire.
(not) at all; (not) in the slightest
nature
natural; right; proper; just; reasonable; appropriate; deserved
abrupt; sudden; unexpected
nature; spontaneity
coincidence; chance; accident; fortuity
inevitable; necessary; certain; sure
just like; (virtually) no different from; (almost) the same as; as good as (e.g. dead, settled)
unnatural; artificial; affected; strained
firmly; flatly; resolutely; decisively; absolutely; definitely
still; as yet; as of old
open; public; official; overt
still; as yet; as it has been
before it happens; previously
natural monument
noisy; confused; uproarious
smallpox; variola
evident; plain; distinct; clear
vague; obscure; indistinct; hazy; ambiguous
nature; Mother Nature
natural gas
natural hot spring
lonely; desolate
inevitable; necessary