然 is one of the most versatile bound morphemes: 虽然 (suīrán, although), 当然 (dāngrán, of course), 突然 (tūrán, suddenly), 自然 (zìrán, nature/naturally), 然后 (ránhòu, then/after that), 居然 (jūrán, unexpectedly).
grammar
然 often functions as a suffix meaning '-ly' or 'in that manner': 忽然 (hūrán, suddenly), 显然 (xiǎnrán, obviously), 果然 (guǒrán, as expected).
